Disgusted by bad Service

I am very disgusted by the level of service Avis rent a car gives me every time I am doing business with them...I rented a car and had a little accident (Tyre had a nail) I was charged an amount to buy a new Tyre...They listed me with their lawyers MBD and they were calling me everyday demanding their R1500.00 which had interest. I finally managed to pay MBD and I asked for a letter that would prove I had paid all monies, I was told I should call AVIS ***...I called this number and a lady Thandi answered the phone and she had a nasty attitude when she told me that the person who writes these letters is on leave and only then I would get the letter. I am unable to buy a car as AVIS had listed me and blocked me from renting from them, and I am being told I should wait till some employee comes back from leave??? what kind of customer service is this??