AVIS Incompetence

Well its actually ridicule, my own vehicle was in an accident and my insurance provided me with a vehicle for the period that it took to do the repairs. The day before delivery of my own vehicle I drove on the N1 and the Mercedes (rental) showed low tyre pressure. I pulled off and replaced the tyre that the indicator was showing as low pressure with the spare wheel, on the following day the car was collected from my house, I signed and indicated that there was a problem with the one tyre on low tyre pressure and I assume it might be a puncture. Since then I have been harassed by collectors relating to a claim of R5000 for the tyre, as it was now pointed out that AVIS does not fix tyres, they replace them. If I had known that I would have driven to the nearest Tiger Wheel and Tyre and have them fix it (cost R100). To make the matter worst, now I have been listed as a slow payer because I refuse to pay the bill whilst my insurance Company hired the car????? Why not fix the tyre or take on the appropriate party????