*****ed by First Car Rental - faulty car, then charged for it!

We received a car at OR Tambo that had tyre pressure issues - both back tyres. When making enquiries about this to their call center, we were advised to check tyre pressure at filling stations periodically - our concern. We subsequently had to change one of the tyres with the spare tyre during our trip. Now we've been charged for a new tyre and claim handling fees, even after providing evidence of communication about this issue (no feedback from First Car Rental to me). Faulty car should be their problem to rectify and NOT make available for rental - could have been serious issues if tyres burst.