I had an amex credit card that I finally paid off and had a nasty surprise a few months later. I got a letter in the mail saying I have been late on my payments and had a big penalty to pay. For some reason when I paid the card off they decided to add on interest right after the fact. So there was about a dollar fifty on the card when I thought I was done with the card that led to a lot bigger balance. I couldn't believe I actually had to go through a fight with them to get those charges dropped!