Pa law prevents anything like this from happening.

If you didn't sign the second deal you could have walked away minus a usage fee, typically like $.40-60 a mile plus taxes and interest. And gotten all you gm card etc back.

On a federal level what they are doing sounds illegal. The truth in lending act is a law, both sides agree to the terms. You signed the new deal out of fear of losing down payment etc. I would still call a lawyer or file a complaint with whatever authority. But since you signed the second deal your probably screwed.