Any Reason to Void the Warranty

We bought a 2014 Hyundai Santa Fe. One of the things I was most attracted to was the 100 000km service plan and the 150 000km / 5 year warranty. I wanted a car that would be reliable and where there would be no nasty, expensive surprises. The car is now less than 3 years old, has only 68 000km on the clock and recently broke down at night on the N12 with the rear differential completely broken apart. I had to get an uber to send my wife and kids home. They have had the car for 2 weeks. Now come back to me to say that the damage was as a result of having a different brand of tyres on the front vs the back. Same size, and spec, but different brand. Firstly I cannot understand how different brand tyres could have such a massive effect. I thought the whole point of a diff was to allow for potential different rotation speeds on different tyres. So the whole scenario feels like they will simply find any reason to get out of doing the repairs.

Because of this they won't cover the R60k repairs under warranty.

The equally frustrating part is that we haven't even changed the tyres - we bought it like that from another car dealer. It has since been serviced by Hyundai, but they failed to mention that having different brand tyres would void the warranty.

My advice to anyone considering buying a Hyundai is DON'T! The warranty is nothing more than a marketing ploy. They will find any reason to get out of paying for mechanical failures on the car.