Did you phone or send a correspondence to Spirit asking for the renewal to be canceled (ahead of the renewal date)? If you felt that the Web site was designed to frustrate your attempt that likely doesn't carry much weight. If you tell Am Ex that you sent notice of cancellation, I would assume Am Ex would reverse the charge. I realize you want the first $39.95 charge revere, but while you're waiting, why not officially terminate the agreement?

A class action lawsuit is a big deal. If you really want to pursue legal methods, you'll have to demonstrate you were misled (just having the renewal in small print won't likely suffice) and that you endeavored to comply with the terms (even by cancelling before the renewal date) but that you could not.

I guess sometimes we DO want government interference in business tactics.