Shocking Customer Service!

Hired a car at Cape Town airport and returned it with a full fuel tank, having refueled at the BP service station at the airport. However, was charged R117 for 6,6 litres of fuel. This was just billed to my credit card with no explanation. Had to phone and request a copy of my invoice. Have disputed the matter with them, but to no avail. Their customer service is shocking. They only got back to me via email even though I have repeatedly called them over a 3 week period. Will never hire a car from them again.