Poor service and incompetence from Avis

I am not happy with Avis . I returned a car beginning of November 2018 and till today the 20th i still have not returned my deposit fee. I have been calling them non-stop and no one is attending or returning to my query. I got the car from Avis Grand central airport in midrand and they are the most useless people ever. I called Avis national customer care and they indicated an IT glitch that took them two weeks to fix, I do not know how is that my problem that their system is not working properly. When i gave them my money, there was no glitch and now i have to get it back there is a glitch. Poor customer service, I am not happy and never hiring a car from them again.