//INSERT INTO Complaint
SqlConnection conn2 = new SqlConnection(ConfigurationManager.ConnectionStrings["ComplaintReportsConnectionString1"].ConnectionString);
conn2.Open();

string query2 = String.Format("Insert Into Complaint(Complaint_Date,Complaint_Details,Type_id,Status_id,Channel_id)VALUES(@Complaint_Date,@Complaint_Details,@Type_id,@Status_id,@Channel_id)", conn2);
SqlCommand cmd2 = new SqlCommand(query2,conn2);

cmd2.Parameters.AddWithValue("@Complaint_Date", TextBox16.Text);
cmd2.Parameters.AddWithValue("@Complaint_Details", TextBox15.Text);

//customerID from customer's table
cmd2.Parameters.AddWithValue("@Customer_id", customerID);

cmd2.Parameters.AddWithValue("@Type_id", type.SelectedValue);
cmd2.Parameters.AddWithValue("@Channel_id", Channel.SelectedValue);
cmd2.Parameters.AddWithValue("@Status_id", Status.SelectedValue);

cmd2.ExecuteNonQuery();
conn2.Close();
Response.Redirect("CustomerComplaint.aspx");