Was the dealer asking for the car back legal if all paperwork was okay?

My boyfriend and I went into a car dealership to try and get a car. Everything was going good until, the salesman asked if we had a bank statement with my boyfriend’s name on it. His name wasn't on the statement so the salesman cut his name off of his pay stub and put it on the bank statement and made a copy. We then drove off the lot with the car. But then the next day someone from the same company called and told us we had to bring the car back even though we signed all the paperwork for everything.