sold a broken car

i bought a polo gti 2007 in march 2015 from pinetown cars and the car started smoking on the first day in my position so i took it back to the dearlership and they told me to run da car in drove it for a week and then they took the car to repair and got the car back after 1.5 months and the car is still smoking and they say i must pay R4500 to buy a warranty so they can sought the problem out.Why should i use my money the dealership suppose to sought all the problems be for selling it.