Nissan stripped my car engine and return it.

On the 10/09/2014, I took my car for repairs at Star Nissan Vereeniging for overheating problem. On the 12/09/2014 I got it back fixed (covered by warranty), but a day after (13/09/2014) it was overheating again. On the (17/03/2014) Star Nissan Vereeniging came and towed the car to their workshop. I was told that I must pay R25 000 for the work to be done as it was removed from the warranty per instruction of Mr Anderson (Service Manager), because it was previously repaired by none nissan approved penalbeater. I must pay R25 000 if I want my car to be fixed. My car is was still under warrenty(Less than three years and 97 000 Km)<br> My concernce