I don't have a dog in this fight, but if I were you, I'd take a copy of that contract to a local district attorney and ask him if they're breaking any laws on intimidation or coercian. Sounds to me like they have an open-ended contract that allows them to change the rules and you're supposed to "fall in line" with whatever they come up with.
Consumer credit laws don't allow a lot of "tricksters" to get by with things they used to be able to do, and you certainly shouldn't have to go to bankruptcy court because these guys think they can just reach in your wallet every time they get another idea. Contracts need to be very specific in whats supplied and who's responsible for payment, and any more, the "extras" probably need to be spelled out as well.
I know if I was getting 1/3 of a class on the bag, I'd tell them I only owed them 1/3 of the payment since I couldn't practice. I'm sure they have you pegged as a troublemaker already, since you bucked up in class and walked out, so you probably won't be getting any specific help in the study of the art.
Seriously, I think I'd look into whether or not they're breaking consumer credit laws with their business, and that should give your lawyer all he needs to get your contract rescinded.
Just a thought.