First USA Bank uses deceptive advertising

First USA Bank (and probably many others) last year converted all existing fixed-rate credit card accounts to a variable interest rate which, not surprisingly, has been steadily going up ever since. They were at least forthcoming, in that they mailed advance notice of their intent to make the change. But anyone, like myself, with a substantial balance had only two options: pay it in full, or accept the changes coming down the pipe. At that time my rate was 9.9%. It has risen three times already this year, and now stands at 13.5%.
I just want to know how First USA defines the word "FIXED", since that is the word which was used to describe the account when I originally applied for the card. My dictionary defines it as "not subject to change; invariant". I understand that there was a provision in the original cardholder's agreement which allowed them to make changes to the account, but what I don't understand is how you can describe something as "fixed", when it is in fact subject to change. This strikes me as somewhat inconsistent, and since it was the term used in the advertisement, I would say somewhat misleading as well. As far as I know, it is illegal to advertise a product in a manner that is intentionally deceptive. If the huge, noticeable print says "this is 'A'", but the tiny, unnoticeable print says "it is really 'B'", I can't see how you can call that anything but an attempt to deceive. I know the government has nailed many other organizations to the wall for advertising practices no different than this, but for some reason banks seem to be immune.
I contacted First USA with my complaint, and was sent a copy of the cardholder's agreement, and a "We're sorry, but you signed it." letter. I also aired my grievence with the Delaware BBB(home state of First USA) and my own state Attourney General, both of whom referred my complaint to First USA. The results were pretty much as I anticipated (i.e, nothing). First USA only sent me another copy of the same letter( as they are required to do by law), and - if you can believe it - a questionaire asking me to rate the quality of their services in the handling of my complaint. Jerks!