Bad service at Kia

I drove my kia optima to Kia, George. Car had 49 000km on the clock. Told them my car is running hot and they must check radiator pipe cause i think there is not water flowing through. Filled in the checklist and wrote there to check radiator pipe and quote to fix. I signed and i left. Week later i got a call and reception lady said that engin needs to be checked for damage and she doesnt know if warranty is going to cover it. She said lets do it and see what warranty department sais. I said sure because there is a warranty, its 5 years or 90 000km. After a few weeks i got an call back from same reception lady. She informed me that the car has been red flagged, the warranty has been removed and that i owe them R15 000 for work done, R158 000 quote, and they will not put my engine back again, its in the boot and i must come and tow the car away. Manager at kia said that they cant see if a cars warranty is in place before hand. They must take engine apart to find that out.... I never signed off on that kind of service. If i knew that i would never of taken the car to them. What can i do?