You have several options, including where the debtor lives.

They may claim you were served or ask the court for permission to serve by publication.

Take anything you get in writing from them to a FDCPA attorney.

Perhaps start with a letter that explains what occurred and asking for an explanation of charges for things you did not get.

The company suing needs to file a dismissal with prejudice.

Consult with experienced consumer rights attorneys on your particular facts. They may be in violation of the FDCPA.

You may be uncollectible and they will not be able get anything from you. Consult with legal aid services.

There are not enough facts to get an idea what may be best. Consult with experienced debt collection defense attorneys.

Such a case is possible but may be difficult. Consult with attorneys who are expert in going after car dealers.

Having provided you with where you can send a check or e-pay, they have fulfilled their obligations.