Sorry for your issue. We had the exact same problem with a truck we purchased 6 years ago. The dealer screwed up on their figures and called the next day pleading for 10,000 more dollars or I could bring it back no questions asked and they would pay the bank back. They would return my trade to me.
I was flabbergasted to say the least. I told them I was sorry for their mistake but that was their problem. The sales manager went off on me. I hung up and called the owner of the dealer and explained the conversation I just had with this guy and if needed he could contact my lawyer. His comment to me was someone owed him 10,000 or they were soon to be without a job.