Check if record Exists then update else insert in Database using GridView in ASP.Net

Hello,

I'm using a gridview that shows purchase order list and a button to inward to stock. I'm using bool value to check if the item from purchase order already exists in the table if yes then the quantity only should get updated else the item should be inserted.

Now the problem is that the loop is continuing even after items are inserted and the quantity is increasing continuously.

Can somebody let me know if there is any mistake in my loop?

    //Below code binds another GridView showing the purchase order item details
    protected void lnkInward_Click(object sender, EventArgs e)
    {
        LinkButton lnkInward = (LinkButton)sender;
        lblInvcNo.Text = lnkInward.CommandArgument.ToString();
        string strQuery = "select * from PurchaseOrder where invcno!='0' and rem!='1' and invcno='" + lnkInward.CommandArgument.ToString() + "' and invcno!=''";
        SqlCommand cmd = new SqlCommand(strQuery);
        DataTable dt = new DataTable();
        SqlConnection con = new SqlConnection(constring);
        SqlDataAdapter sda = new SqlDataAdapter();
        cmd.CommandType = CommandType.Text;
        cmd.Connection = con;
        con.Open();
        sda.SelectCommand = cmd;
        sda.Fill(dt);
        divInvcDetails.Visible = true;
        divPOList.Visible = false;
        grdInvcDetails.DataSource = dt;
        grdInvcDetails.DataBind();
    }

    //Below code uses bool value to check if the item already exists in the database. If exists, will call inwardUpdate();  else, will call inwardConfirm();
    protected void btnInward_Click(object sender, EventArgs e)
    {
        bool exists = false;
        foreach (GridViewRow invcdetailsrow in grdInvcDetails.Rows)
        {
            Label ITEMNAME = invcdetailsrow.FindControl("lblItemname") as Label;
            Label HSN = invcdetailsrow.FindControl("lblHsn") as Label;
            Label QTTY = invcdetailsrow.FindControl("lblQtty") as Label;
            Label MRP = invcdetailsrow.FindControl("lblMrp") as Label;
            Label SGST = invcdetailsrow.FindControl("lblSgst") as Label;
            Label CGST = invcdetailsrow.FindControl("lblCgst") as Label;
            Label DISC = invcdetailsrow.FindControl("lblDisc") as Label;
            using (SqlConnection CheckCon = new SqlConnection(constring))
            {
                CheckCon.Open();
                string CheckQuery = "select count(*) from [Stock] where itemname = @itemname";                
                using (SqlCommand CheckCmd = new SqlCommand(CheckQuery, CheckCon))
                {
                    CheckCmd.Parameters.AddWithValue("@itemname", ITEMNAME.Text);
                    exists = (int)CheckCmd.ExecuteScalar() > 0;
                }
                if (exists)
                {
                    inwardUpdate();
                    divInvcDetails.Visible = false;
                    divPOList.Visible = true;
                }
                else
                {
                    inwardConfirm();
                    divInvcDetails.Visible = false;
                    divPOList.Visible = true;
                }
                CheckCon.Close();
            }
        }
    }
    //Below code is used when item already exists in the database and only quantity will increase
    protected void inwardUpdate()
    {
        foreach (GridViewRow invcdetailsrow in grdInvcDetails.Rows)
        {
            Label ITEMNAME = invcdetailsrow.FindControl("lblItemname") as Label;
            Label HSN = invcdetailsrow.FindControl("lblHsn") as Label;
            Label QTTY = invcdetailsrow.FindControl("lblQtty") as Label;
            Label MRP = invcdetailsrow.FindControl("lblMrp") as Label;
            Label SGST = invcdetailsrow.FindControl("lblSgst") as Label;
            Label CGST = invcdetailsrow.FindControl("lblCgst") as Label;
            Label DISC = invcdetailsrow.FindControl("lblDisc") as Label;
            using (SqlConnection InwardCon = new SqlConnection(constring))
            {
                string InwardQuery = "Update Stock set qtty=CAST(IsNULL(qtty, '0') as int) + '" + Convert.ToInt32(QTTY.Text) + "' where itemname = @itemname;";
                InwardCon.Open();
                using (SqlCommand InwardCmd = new SqlCommand(InwardQuery, InwardCon))
                {
                    InwardCmd.Parameters.AddWithValue("@itemname", ITEMNAME.Text);
                    int i = InwardCmd.ExecuteNonQuery();
                    if (i > 0)
                    {
                        ScriptManager.RegisterStartupScript(this, this.GetType(), "swal", "swal('Stock Updated!', 'Vinod Enterprises, Vijayapura', 'success');", true);
                        UpdatePOInwarded();
                        BindPOList();
                    }
                }
                InwardCon.Close();
            }
        }
    }
    //Below code is used when item does not exist in the database and an insertion will take place.
    protected void inwardConfirm()
    {
        foreach (GridViewRow invcdetailsrow in grdInvcDetails.Rows)
        {
            Label ITEMNAME = invcdetailsrow.FindControl("lblItemname") as Label;
            Label HSN = invcdetailsrow.FindControl("lblHsn") as Label;
            Label QTTY = invcdetailsrow.FindControl("lblQtty") as Label;
            Label MRP = invcdetailsrow.FindControl("lblMrp") as Label;
            Label SGST = invcdetailsrow.FindControl("lblSgst") as Label;
            Label CGST = invcdetailsrow.FindControl("lblCgst") as Label;
            Label DISC = invcdetailsrow.FindControl("lblDisc") as Label;
            using (SqlConnection InsertInwardCon = new SqlConnection(constring))
            {
                string InsertInwardQuery = "insert into Stock(itemname, hsn, qtty, mrp, sgst, cgst, disc, status, rem) values(@i1, @i2, @i3, @i4, @i5, @i6, @i7, @i8, @i9);";
                InsertInwardCon.Open();
                using (SqlCommand InsertInwardCmd = new SqlCommand(InsertInwardQuery, InsertInwardCon))
                {
                    InsertInwardCmd.Parameters.AddWithValue("@i1", ITEMNAME.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i2", HSN.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i3", QTTY.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i4", MRP.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i5", SGST.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i6", CGST.Text);
                    InsertInwardCmd.Parameters.AddWithValue("@i7", "0");
                    InsertInwardCmd.Parameters.AddWithValue("@i8", "1");
                    InsertInwardCmd.Parameters.AddWithValue("@i9", "0");
                    int pmj = InsertInwardCmd.ExecuteNonQuery();
                    if (pmj > 0)
                    {
                        ScriptManager.RegisterStartupScript(this, this.GetType(), "swal", "swal('Inward Successful!', 'Vinod Enterprises, Vijayapura', 'success');", true);
                        UpdatePOInwarded();
                        BindPOList();
                    }
                }
                InsertInwardCon.Close();
            }
        }
    }
    //Below code is to set remove status to 0 after inward process
    protected void UpdatePOInwarded()
    {
        using (SqlConnection con = new SqlConnection(constring))
        {
            string query = "Update PurchaseOrder set rem='1' where invcno=@invcno";
            con.Open();
            using (SqlCommand cmd = new SqlCommand(query, con))
            {
                cmd.Parameters.AddWithValue("@invcno", lblInvcNo.Text);
                cmd.ExecuteNonQuery();
            }
            con.Close();
        }
    }

Please help!