I have had so many similar issues with Avis. If they charge my card in error I usually contact them and give them one opportunity to resolve. If they insist on putting me in their usual spiralling holding patterns I will call my card company and get the money back myself. All credit card companies have procedures in place for unauthorised transactions, and that is what this is - unauthorised. It is then up to Avis to work hard to claim the money back from me if they believe it is justified, not for me to work hard to rightfully get my own money back.