Getting a refund fon Rental Deposit from Avis is a hussle

I rented a vehicle with Avis on month to month basis effective 17 0ct up to 20 Dec 2024. I ended the lease on the 20th December 2024 and returned the vehicle same day. I received credit invoice of how much I will be getting back from my rental deposit. Today is the 6th of January 2025 I have not received a cent of that money. I called Avis customer care they said I must wait 10 working days, I did that but still nothing I called my bank, the bank said that can't release them held funds without an authorisation letter from the merchant. I am so disappointed I thought Avis was a reliable rental company with effective systems in place.