Sixt/First car rental Lanseria, shoddy over fuelling and billing and mechanically poor cars

Sixt/First car rental Lanseria - Got a car that had brake, accelerator and performance issues. Despite refueling it just before returning and providing invoice confirming same, still got billed for additional fuel and admin. When I queried this this company claims they needed to add R52 of fuel (about 2Liters). The filling station I used is 10km from this place, therefore it would have used 600ml of fuel (R15) as it is rated at 16.5km/l Honda WR-V between the filling station and this place. Nice way for them to make additional R100 on each rental quickly. Also, I had to log a complaint for the more than double difference amount to be refunded on my card. Had to go and find someone to check the car upon return. I rent a lot of cars and this is the worst rental experience I have had in a really long time.