My personal thoughts.
I would suggest to them an easy payment plan.
You could file a civil action but you would waste the filing fee as the court in your state would have no personal jurisdiction over the defendant and the case would be tossed. The only way the court could find personal jurisdiction is under a long arm statute and you would have to research the law on that and see if the defendant's actions are covered by the long arm statute. You would probably have to prove that in court, especially if the defendant answers with that affirmative defense.
You would also have to have a physical address for the defendant and have that person served after filing.
You should consult a local attorney. You often can get an initial consultation for free.

