Avis rental South Africa

I thought to save money and drive up from Bloemfontein to OR Tambo airport to board our international flight there. Trying to do everything by the book I filled up the car at the Engen at OR Tambo and dropped the car at Avis at the airport, Driving just a few hundred meters from the refueling to the drop. When I received my invoice I noticed a refueling service charge of R3652.17 and R60.41 for 2.63 liters of petrol. On complaining to customer service and supplying the refueling slip as evidence they decided graciously to credit me back with R100.42 ignoring the refueling service charge completely. When visiting the local Avis at Bloemfontein they assured me that it was referred to their manager. Nothing happened. After a few days I called Avis customer care and they said I should follow it up with the local branch and the Gauteng branch creating the impression that these are separate entities. I tried the email route, they simply stopped responding( Do not believe the turnaround promise of 24h) The only option left is to open a dispute from my credit card provider. I am just astonished that an international company can stoop so low in admin and customer care . Please only use Avis as a last resort, they seem to have grouped themselves with all the other disreputable car rental companies.