Legal Question in Credit and Debt Law in Pennsylvania

Yes you can file that. As far as how you go about doing that, that's a pretty hefty question for a free advice forum.

Statute of limitations is an affirmative defense that is raised in your answer to the complaint. Did you do that? While this case is in arbitration what efforts have you made to engage in discovery? Any? What evidence do you have to support the fact that the last payment on the account or the due date for the payment was 4 or more years ago?

You can allege whatever you want in your motion. However, you have to be able to prove it by providing some evidence and you have to allow the other side the opportunity to refute this if they can.

I suggest that you hire local counsel prior to your arbitration date. If you really do have a valid defense like statute of limitations then getting an attorney will be well worth it. If you represent yourself and do not do the proper things to assert the defense then the defense will be considered and it will not matter as a judgment may be entered against you. At the very least, I would get a consult with an attorney.