Thanks for your input! I should have mentioned that I already did file a claim online on Sunday (early EST) with Amex, after speaking to them on the phone. I would never have thought to dispute the claim but the agent seemed to think it was the best option, almost made it seem like standard procedure. That said, it would be ideal if Avis just fulfills their obligations to Amex and supplies them with the necessary documents without having to file a dispute! So maybe I will wait for a bit and just see if it gets resolved as it should.