Fifth Third Bank Convenience fee ripoff Cincinnati Ohio

Every month, I send in my monthly instalment of my mortgageto Fifth Third bank, Cincinnati Ohio through the US Post Office. Recently, I tried to make that payment over the phone but the bnk employee who answered the phone told me that if I made a payment over the phone, the bank would charge me a "Convenience fee" of       $ 15. He explained that this fee was to cover the possibility of fraud. I fail to understand how gouging me $15 would prevent any fraud. This is just one more way of ripping off a customer.