credit card companies pull that crap all the time too. Anytime you get a credit card statement, be sure to read any fine print that's not part of what you normally get. Sometimes it says "Hello loyal customer, we've decided to jack your interest rates for absolutely no good reason, and unless you call us and complain, it'll be effective starting next month. Consider yourself legally notified."
I've been through that particular stunt more than once. It's not unusual, it's just "good business". So get used to it, and stay vigilant.