Poor account billing- Billing for costs not incurred

I have been using Woodford car-hire for the last 13 months. I have always been happy with their service but lately in the last 4 months I constantly have issues with the billing on my invoices. I reported this to their customer care, where they billed me for tollgates where I haven’t even drived on my latest invoice they billed me R49747, for 8300km where I only drove about 1300km which falls within the 100km free, included on my contract. This was a new car which still had paper number registration plates and when I returned the car the odometer reading was about 1700 km. I expect an a and refund, from the MD of Woodford as well as a refund on the interest incurred on my credit card. You have a great company don’t let negligence on your account, ruin your reputation.