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I have a feeling what they did was "pay" to get the car repaired then added that amount to your balance. They have to disclose this to you.
Was this a new car loan or a used car?
Check the lemon laws in your state.
I would find out the above info then get a free consult with an attorney in your area.
Ditto to everyone else.
Unless you are willing to pay for the full balance, consult an attorney.