I would say screw them and return the car. It is in your favor because they want to sell you the car if they can. I think they are playing with you because you do not have much experience in this matter. if you do return the car, you must get equal value for your old car - If they refuse to pay the fair amount, you have the right to take this matter to small claims court and settle it through a judge (which does not cost you much because lawyer is not involved in this)