See if you find something fishy about these lines of code:
Code:
                    command.Parameters("firstName").Value = customer.FirstName
                    command.Parameters("lastName").Value = customer.LastName
                    command.Parameters("lastName").Value = customer.address
                    command.Parameters("lastName").Value = customer.phoneNumber
Hint: copy/pasting can save a lot of time. But you have to make sure you actually update everything.

I once saw a study where a guy wrote a bot to analyze thousands of GitHub projects for copy/paste errors. The fascinating finding was not how many he found, but how dramatic the probability swayed towards the last line being the error.

In this case, it's more than the last line.