Complain about poor service of a car dealership.

I bought a car yesterday at Anglo car dealership cash, which was R100000 and they offered a discount of R5000. After the deal deal was signed and sealed, I took of with the car only to find out the car has a problem along the way back home. I tried to contact them but it was after office hours. Today I took the car to the mechanic to diagnose it only to find that it has a problem with cylinder head casket and is starting to mix oil and water. Contacted the dealership againg to report the matter and they tell me that they can't help me in that regard.