Update Checked GridView Row in database and send SMS and Email using C# in ASP.Net

how to make Y update in table and sms and email not send after update Y in table

SqlConnection con = new SqlConnection(@"Data Source=(localdb)\Projects;Initial Catalog=Employee;Integrated Security=True;Connect Timeout=30;Encrypt=False;TrustServerCertificate=False");
protected void Page_Load(object sender, EventArgs e)
{
    if (Session["FirstName"] == null)
        Response.Redirect("login.aspx");
    else
    {
        String EmplooyeId = Convert.ToString((int)Session["empid"]);
        String FirstName = Session["FirstName"].ToString();
        String LastName = Session["LastName"].ToString();
        String Department = Session["Department"].ToString();
        lbluserInfo.Text = "Department:- " + Department + ".";

        Label1.Text = "Welcome, " + FirstName + " " + LastName + ".";
    }

    if (!Page.IsPostBack)
    {
        BindEmpGrid();
    }
}
protected void BindEmpGrid()
{
    SqlCommand cmd = new SqlCommand("select * from email", con);
    DataTable dt = new DataTable();
    SqlDataAdapter adp = new SqlDataAdapter(cmd);
    adp.Fill(dt);
    grEmp.DataSource = dt;
    grEmp.DataBind();
}

protected void btnSendMail_Click(object sender, EventArgs e)
{

    string Id = string.Empty;
    DataTable dt = new DataTable();
    try
    {
        foreach (GridViewRow row in grEmp.Rows)
        {
            CheckBox cb = (CheckBox)row.FindControl("chkSelect");

            if (cb.Checked == true)
            {
                if (cb != null && cb.Checked)
                {
                    //get Current EMAIL_ID from the DataKey
                    Id = Convert.ToString(grEmp.DataKeys[row.RowIndex].Value);
                    SqlCommand cmd = new SqlCommand("select email, txn_desc, amt, phone from email where Id=" + Id + "", con);
                    SqlDataAdapter adp = new SqlDataAdapter(cmd);
                    //Fill datatable with EMAIL_ID corresponding to Current EMP_ID
                    adp.Fill(dt);
                    //Get EMAIL_ID into variable
                    string emailId = dt.Rows[0]["email"].ToString();
                    string txn_desc = dt.Rows[0]["txn_desc"].ToString();
                    string amt = dt.Rows[0]["amt"].ToString();
                    string phoneNo = dt.Rows[0]["phone"].ToString();

                    //write code to send mail
                    SendEmailUsingGmail(emailId, txn_desc, amt);
                    sendSMS(phoneNo.Trim(), "Amount of Rs " + amt + " for " + txn_desc + "is sent to your Bank account");
                    dt.Clear();
                    dt.Dispose();
                }
            }
        }
        ScriptManager.RegisterClientScriptBlock(Page, Page.GetType(), Guid.NewGuid().ToString(), "alert('Payment Details Sent Successfully');", true);
    }
    catch (Exception ex)
    {
        Response.Write("Error occured: " + ex.Message.ToString());
    }
    finally
    {
        Id = string.Empty;
    }
}

private void SendEmailUsingGmail(string toEmailAddress, string txndesc, string amount)
{
    try
    {
        SmtpClient smtp = new SmtpClient();
        smtp.Credentials = new NetworkCredential("indradeo7306@gmail.com", "7503431478");
        smtp.Port = 587;
        smtp.Host = "smtp.gmail.com";
        smtp.EnableSsl = true;
        MailMessage message = new MailMessage();
        message.From = new MailAddress("indradeo7306@gmail.com");
        message.To.Add(toEmailAddress);
        message.Subject = " PAYMENT INFORMATION";
        message.Body = "Amount of Rs " + amount + " for " + txndesc + "is sent to your Bank account";
        smtp.Send(message);
    }
    catch (Exception ex)
    {
        Response.Write("Error occured: " + ex.Message.ToString());
    }
}

protected void chkSelectAll_CheckedChanged(object sender, EventArgs e)
{
    CheckBox chkAll =
        (CheckBox)grEmp.HeaderRow.FindControl("chkSelectAll");
    if (chkAll.Checked == true)
    {
        foreach (GridViewRow gvRow in grEmp.Rows)
        {
            CheckBox chkSel =
                    (CheckBox)gvRow.FindControl("chkSelect");
            chkSel.Checked = true;
        }
    }
    else
    {
        foreach (GridViewRow gvRow in grEmp.Rows)
        {
            CheckBox chkSel = (CheckBox)gvRow.FindControl("chkSelect");
            chkSel.Checked = false;
        }
    }
    if (chkAll.Checked == true)
    {
        string flag = chkAll.Checked ? "Y" : "N";
        string constr = ConfigurationManager.ConnectionStrings["constr"].ConnectionString;
        using (SqlConnection con = new SqlConnection(constr))
        {
            SqlCommand cmd = new SqlCommand("UPDATE email SET flag = @flag where Id=@Id");
            cmd.Connection = con;
            cmd.Parameters.AddWithValue("@flag", flag);
            con.Open();
            String isUpdated = Convert.ToString(cmd.ExecuteNonQuery());
            cmd.ExecuteNonQuery();
            con.Close();
        }
    }
}

static string sendSMS(string mobileNo, string messageTxt)
{
    string SMSurl = "gateway";
    WebRequest request = HttpWebRequest.Create(SMSurl);
    WebResponse response = request.GetResponse();
    string retString = response.ToString();
    response.Close();
    return retString;
}

protected void LinkButton16_Click(object sender, EventArgs e)
{
    Response.Redirect("login1.aspx");
}