Did American Express specifically say the interest rate increase was because of the returned check? Credit card companies are doing a lot of shady stuff in this economy - raising interest rates, adding annual fees to cards, etc. I'd call one more time and say that since you met the payment deadline you don't believe your interest rate should be increased. If they don't give in, close your card (you can still pay it off while it's closed) and use another no-fee, lower interest card. I don't think you should ever have to pay for your credit if you're paying off your bills (interest aside, of course). On a related note, everyone watch your mailbox for "junk mail" from credit card companies. They may be adding fees to your card, hoping you don't notice. link