Dissatisfaction with Thrifty car rental

As an South African working and living abroad, I have to rely on car rental companies to get going in SA, and I've tried a number of companies and found Thrifty to be the better company. However my most recent experience with them left me totally disgusted and with a rather bad taste in my mouth. We hired a vehicle at OR Tambo on Monday 27 August 2018, and returned the vehicle on Monday 02 September . Upon collecting the vehicle, nobody accompanied us to the vehicle, as is usually the case and after I loaded the luggage in the vehicle, I walked around the vehicle myself to check if the items marked on their silhouette corresponds with what is noticeable. Everything was fine, accept the right rear wheel seemed a bit lower in pressure compared with the others, but with luggage weighing around 50kg, I thought nothing of it. When I reached my destination in Brooklyn PTA , and with the luggage offloaded, the R/R wheel clearly had a slow puncture and we decided to have the spare wheel fitted instead, to be on the safe side. Both the spare wheel and R/R wheel clearly had punctures plugged as we found evidence of that. As I dropped the vehicle off on Monday 2 September, I mentioned to the person at the drop off point that it had a slow puncture, and that I had the spare wheel fitted. They asked me to fill in a form to report it, but they gave me an accident claim form to fill in and I asked why if it was only a slow puncture, and the lady assured me this was to report the slow puncture. Needless to say they debited my credit card with an amount of R1748, and when I queried this, they said because I filled in the Accident Claim form. I immediately appealed and have been trying ever since to get this matter seen to by higher authority, but they simply just ignore my appeal. Where do I go with this now? I'm convinced I received a car with a slow puncture and no have to pay for this.