Happened to me with my new pickup truck. Dealer said they mis-calculated and I owed them another $1000. I told them I was sorry for their error. The threatened to come get it. And threatened to refuse the 0% financing. My response was, I had the signed contract and sales agreement. And I had the vehicle. I had verified their numbers twice. If they cancel the financing, I won't need to pay the loan. They would be having their attorney contact me. And they never did have them call. Never heard from them again.
In your case your sales agreement was 15% less than their asking price. That dealer really sucks. You are WAY to understanding.