WILLIAMS HUNT DIS-SATISFIED CUSTOMER

I sent my Hummer To Williams Hunt Fourways on the 12 May 2015 with a complaint of AC off.They sent me a Estimate and I let them do everything except front fender and lamps.I received my car back and evrything was fine.Two days later I have same problem with AC Off. I returned my car back to Williams Hunt Fourways with the complaint that it is double labour and then they said they can not help in that regard.They then told me my Thermostat needs to be replaced and i agreed and they replaced the thermostat on 19 May 2015.This is now after i had to take it back for AC Off!!! I paid Williams Hunt Fourways and fetched my car on 20 May 2015.As I arrived at my business I see the temperature is very high...this is same day.I took it back to William Hunt Fourways on the 22 may 2015.They phoned me and said it is a faulty Thermostat and that my waterpump needs to be replaced and that my gasket is blown!!!!!what am i supposed to do regarding the damage after they inform me telephnically about faulty thermostat and the overheating started after they replaced the thermostat.Should i Pay for this????!!!