Thrifty Car Rental

I hired a car at OR Tambo International. Felt like the aircon was working in the coolness of the airport car park but once I got on the road to Mookgopong (Naboomspruit) in 32 degree heat it very quickly became evident that the aircon was infact not working at all. When I returned the vehicle I told the attendant that the aircon wasn't working and he made a note on the window. I sent an email asking for some sort of refund because I paid for a car with aircon and I didn't get what I paid for. Their response was that the aircon was working. I had friends with me in that car most of the weekend so I have witnesses to the contrary. I advised them that I was not happy with the outcome and have sent 2 consequent emails but have had not further response from them.