Refund from AVIS

I rented a car from avis from 23rd May to 6 June. Returned the car in good condition and fuel filled up. I was told my refund will take 3-5 days and 11 days later I am still waiting. I have reached out to the bank and they are asking for a letter from Avis. Now AVIS is saying they cant provide this letter because my account was debited by them and no letter is required. Question is what do I do now because I need my deposit. Why isn't any of the parties taking accountability. I need my refund