I both a car and they ended repoing it can i get my money back or what can i do?

the dealership made alot of things that we didnt know they cross my co signers name without us knowing the car turned off a day later they told us they didnt care what happen cuz they had got there money. they repo the car and they said that the dealership wanted the car back can i get my downpaiment back what can i do to get it ?