Writing to a SQLite Database in C#

Using Visual Studio/ Windows Forms, I am trying to write data to a SQLite DB. The Event handler for the "submit" button is supposed to take the information in the relevant textboxes and write them to the corresponding fields in the DB. The database connection and location is handled in the dbConnect class, and works as the login form works. When the submit button is clicked however, nothing happens, no error message, nothing. Can you see anything glaring?

private void button2_Click(object sender, EventArgs e)
        {
            try
            {
                //write new customer data to db
                using (SQLiteConnection dbcon = new SQLiteConnection(conString))
                {
                    dbcon.ConnectionString = dbConnect.source;
                    string sql;
                    {
                        sql = "INSERT INTO guest(forename,surname,telnumber,email,address)"
                            + " Values(@f,@l,@tel,@em,@ad)";
                    }
                    using (SQLiteCommand cmd = new SQLiteCommand(sql, dbcon))
                    {
                        cmd.Parameters.AddWithValue("f", foreTB.Text);
                        cmd.Parameters.AddWithValue("l", surTB.Text);
                        cmd.Parameters.AddWithValue("tel", telTB.Text);
                        cmd.Parameters.AddWithValue("em", emailTB.Text);
                        cmd.Parameters.AddWithValue("ad", addTB.Text);

                        //perform db operation
                        dbcon.Open();
                        cmd.ExecuteNonQuery();
                        dbcon.Close();
                    }
                }
                //display relevant action feedback message
                {
                    showlabel("New Customer Added OK", 4000);
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine("An error occurred: '{0}'", e);
            }
        }