Purchase of a vehicle

I purchased a used Subaru, signed the papers and drove away with the car. The dealership is now contacting me stating that I need to give a down payment. The bank they got my loan with will not fund the loan with out money down. Isn't it too late for that? I already signed all the paperwork without anything down, and I have the car.

Anyone have any advise?

Do you have the title for the vehicle?