Well, of course you can file a lawsuit...you're an American, that's what we do best.
But I don't think it will do anything, and usually lawsuits like that end up costing far more than $15 a month...but yeah, I'm pretty sure you could find a lawyer somewhere to file a lawsuit for you. Have you tried to contact the company? Are they aware of the problem? Why ARE you still paying $15 a month for a service you can't use? Maybe they'll comp you a few months free while they fix the problem. Who knows. Is it just you, or are other players having problems, too?
(I dunno, though. If I were a judge, and if I were handed a lawsuit about not being able to log in three times a week for a computer game, I probably would just toss it out and maybe fine you a couple hundred dollars for wasting my time. That's just because I don't value computer games, so nothing personal, just my two cents.)
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Superman wears Jack Bauer pajamas.