Access Control in Static WebMethod Error: object refrence not set instance of object

How to get control in static webmethod.

it show error object refrence not set instance of object 

how can i do this tell me right solution to perform this

OPD is my page name

[WebMethod]
public static string GetCustomersInfoRegiidOpdod(string regids, string opdids)
{
    OPD op = new OPD();
    op.getCustomerRecords(regids, opdids);      
    return null;
}

so i make i instance of my page to call a function getCustomerRecords()

    protected void getCustomerRecords(string regids, string opdids)
    {
        string regdno = regids.ToString();
        setcontrol();        
        DataTable RegDetails = SqlObject.get_info_Patient(regids, opdids);
        //AAA---------------------
        global.regid = regids;
        
        txtregistrationno.Text = regids;

        txtname.Text = RegDetails.Rows[0]["patientname"].ToString();
        //DateTime date = DateTime.ParseExact(RegDetails.Rows[0]["date"].ToString(), "dd/MM/yyyy", CultureInfo.InvariantCulture);
        txtdate.Text = Convert.ToDateTime(RegDetails.Rows[0]["date"]).ToString("dd/MM/yyyy");

        if (RegDetails.Rows[0]["age"].ToString() != "0")
        {
            txtage.Text = RegDetails.Rows[0]["age"].ToString();

        }

        if (RegDetails.Rows[0]["contactno"].ToString() != " ")
        {
            txtnumber.Text = RegDetails.Rows[0]["contactno"].ToString();

        }
        txtopdnum.Text = opdids;

        drop_gender.SelectedValue = RegDetails.Rows[0]["sex"].ToString();
        ddlmarried_status.SelectedValue = RegDetails.Rows[0]["mstatus"].ToString();
        ddl_occupation.SelectedValue = RegDetails.Rows[0]["occupation"].ToString();
        if (RegDetails.Rows[0]["address"].ToString() != " ")
        {
            txtaddress.Text = RegDetails.Rows[0]["address"].ToString();

        }

        //global records all data regarding patient
        string regid = regids;
        string opdid = opdids;
        DataTable dt = SqlObject.get_All_record_regarding_patient(regid, opdid);

        //presentingComplaints
        DataTable dt1 = new DataTable();
        DataView dv = new DataView(dt);
        dv.RowFilter = "vtype='pc'";
        dt1 = dv.ToTable();
        ViewState["presentingcomplaints"] = dt1;
        var count = dt1.Rows.Count;
        if (count == 0)
        {

        }
        else
        {
            DataRow dr = (DataRow)dt1.Rows[dt1.Rows.Count - 1];
            var d = dr["id"];
            ViewState["Number"] = 0;
            GridView1.DataSource = dt1;
            GridView1.DataBind();
        }
    }