Here bill number does not increment after 10. Please help!! Urgent!

private void cashreciept_Load(object sender, EventArgs e)
      {
            SqlDataAdapter da = new SqlDataAdapter("SELECT TOP 1 [Bill No] FROM cashreceipt ORDER BY [Bill No] DESC", sq.connection());
            DataTable dt1 = new DataTable();
            da.Fill(dt1);
            if (dt1.Rows.Count > 0)
            {
                billno = Convert.ToInt32(dt1.Rows[0][0]);
                
                billno +=1;
                txtbill.Text = billno.ToString();
            }
            else
            {
                string h = "1/1/1911";
                string c = "insert into cashreceipt values('" + 0 + "','" + 0 + "','" + 0 + "','" + 0 + "','" + 0 + "','" + 0 + "','" + h + "')";
                SqlCommand ccmd = new SqlCommand(c, sq.connection());
                ccmd.ExecuteNonQuery();
                SqlDataAdapter da1 = new SqlDataAdapter("SELECT TOP 1 [Bill No] FROM cashreceipt ORDER BY [Bill No] DESC", sq.connection());
                DataTable dt2 = new DataTable();
                da1.Fill(dt2);
                if (dt2.Rows.Count > 0)
                {
                    billno = Convert.ToInt32(dt2.Rows[0][0]);
                    billno  = billno+1;
                    txtbill.Text = billno.ToString();
                }

            }
        }