You don't want to go through arbitration for this. Disclosure: I am a FINRA arbitrator. I would be the type of person who ends up on a panel to decide these things. Arbitration isn't a good place to go pro se on anything and it isn't speedy. I've got hearings just coming up for cases that were started on an "expedited" basis back two years ago.
You're going to come out ahead by escalating your problem a reasonably high point (this may take written letters) and showing whatever it is that they want to prove that you're not attempting fraud.