Poor service from Capetown international branch

I rented a car at Capetown international, had the car for between 6 to 8 hours only, they charged me for 1500kms for that time, I called the lady Yumkela and Akona from their Capetown branch both promised me to resolve the issue but till now not even a courtesy call, very poor service for a big company like avis, it's a shame that they over charged us then play dead to refund, this is theft!