What do you do with a car that was voluntarily reposesed and the bank never picked it up?

The simple answer is, that if the bank never picked it up it is not repossessed. If you are not making your payments, and really want to give up the vehicle, what a lot of people do is take it back to the bank, and leave it in their parking lot. Be sure to give the bank manager the key and let them know what you are doing. If this is not possible continue to try to call them.