GOOD YEAR TYRES - NEVER AGAIN

I had 2 SAVAS tyres (budget tyres made by Goodyear) fitted to a Renault Scenic 3 years ago (tyres date stamped 2015 - 5 year structural guarantee). One of the tyres has developed 3 holes (about 1mm x 5mm each) on the inside next to the rim. Neither the guys at SUPERQUICK or TYRE MART had seen anything like this. Goodyear sent a rep to look, she took photos of the holes and sent them to their technical guys. Verdict was they are stress cracks caused by overloading. I have seen stress cracks in tyres (quite common), I GOOGLED stress cracks in tyres and the holes (not cracks) look nothing like them. The car has not been overloaded EVER - the tyres were on the front of the car so overloading would have has minor effect on them and only one tyre is showing the holes?? I am a petrol head, I know about cars and tyres and it is an insult to my intelligence thinking I will just accept their ridiculous verdict.