American Express Allowed me to exceed credit line without my authorization and then raised interest rate 190% for going over limit.250% El Paso, Texas

American Express permitted me, without my authorization, to exceed my credit limit.   Then it raised my interest rate from 14.24% to the default rate of 27.24% because I remained over limit for two months as a result of making the minimum payments the billing statements required.   As I understand the Credit Card Reform Act of 2009, they need prior authorization from the card holder to permit the card holder to go over limit in the first place.   Unfortunately, I am sole proprietor of a very small business and had a business card. Business cards apparently are exempt from the Credit Card Reform Act. I didn't notice the increase for a few months (mea culpa for not paying closer attention), but closed the account as soon as I discovered the new rate and AmEx said there was nothing it could do.   To add insult to injury, I then paid the balance off in full, but AmEx has just billed me for interest calculated on that balance, even though its billing statement says you can avoid interest charges by paying in full before the end of the billing cycle, which I did.