Update multiple columns from code behind in ASP.Net

please this update query sets update on one row, but i want to update SET Dept=@Dept And Credit=@Credit

here is my query

                                            if (inserted > 0)
                                            {
                                                float updatedebt = olddebt + grandtotal;
                                                float sum = updatedebt;
                                                using (SqlConnection con = new SqlConnection())
                                                {
                                                    con.ConnectionString = str;
                                                    using (SqlCommand cmd = new SqlCommand())
                                                    {
                                                        cmd.CommandType = CommandType.Text;
                                                        cmd.Connection = con;
                                                        cmd.CommandText = "UPDATE CustomerDetail SET Debt=@Debt WHERE CustomerPhone = @CustomerPhone";
                                                        cmd.Parameters.AddWithValue("@PaymentStatus", paymentstatus);
                                                        // cmd.Parameters.AddWithValue("@AmountPaid", txtamountpaid.Text.Trim());
                                                        cmd.Parameters.AddWithValue("@Debt", updatedebt);
                                                        //  cmd.Parameters.AddWithValue("@Balance", grandtotal);
                                                        cmd.Parameters.AddWithValue("@CustomerPhone", ddlcustomerphone.SelectedItem.Text);
                                                        con.Open();
                                                        inserted = cmd.ExecuteNonQuery();
                                                        con.Close();
                                                    }
                                                }
                                            }
                                            BindProductsSells();
                                        }