Avis retains deposits for months. Repeated follow-ups required.

I rented a car from Avis on the 4th of October. I paid a vary high deposit - higher than other rental companies. They are still keeping a hold on this deposit. Every time I call them (three times now), they tell me they have to confirm with my bank that the bank is holding the amount!!!! Apparently they don't have access to their own records. Only once the bank confirms this, Avis will issue an instruction to the bank for the refund of my funds. Each time I call Avis they say it will take another five working days. I was also told not to get upset because all Avis clients post September 2018 with the same major bank has the same problem. As if that makes it ok. Nobody has even bothered to apologize or follow-up.