Incorrect Billing

On the 13th of Dec 2018 I hired a car Polo Vivo which had a tyre burst on the 15th while I was on my way to Port Alfred for my sister’s white wedding, I phoned Europcar requesting a spare wheel and I was told that they don’t have spare wheels but they will bring me another car in Port Alfred the following day. On the 16th in the morning a guy brought another car Renault Clio so we swapped the cars and he left. Later that day the car was almost on quarter full already before I even travelled back to Port Elizabeth so I refueled it and unfortunately I paid cash and I didn’t keep the slip because I wasn’t returning the car yet just that when I am travelling I always prefer so start my journey with a full tank, bear in mind the car was parked at the hotel since it was brought to me I only took it when I was going back to PE. I drove back to PE and the following day on the 17th I had to drive to Peddie for my sister’s traditional wedding so as usual I refueled the car And I also refueled it refueled it when I was returning it. After returning the car I received an invoice and on that invoice I was billed for fuel of that Polo whereas the guy brought me a car that wasn’t full. I phoned Europcar and the lady that I spoke to promised to call me back but she never did. Again on the 1st of July 2019 I hired a car Renault Clio. When I took it had spanel message on the dashboard but since the guy that was inspecting it said it’s new so I thought everything is fine. The day before the return date it showed “Check Injection” message on the dashboard then I called Europcar and they said I must Go and change it. Before changing it I refueled it at the petrol station next to PE Airport then I returned it and I was given a Polo Vivo which I also refueled the following day before returning it. But they have billed me money for refueling. I want my money back, they keep on robbing me and I can’t take it anymore. I sent them an email but I haven’t received any response.