Pirelli tyres SWAK

I bought 4 new tyres for my bmw x3 last year November and by mid August I noticed that my rear tyres looked like slicks. I then worked out the km i got out of it for in less then a year it was +- 18000 km. The front tyres looks perfect but rear tyres are bad. Pirelli rep mr Donald said after inspection the refuse to replace the tyres, reason being that there is no material defect. Well here a defect I think bmw sa should not recommend Pirelli tyres on any bmm. Thanks to the guys of bmw Durbanville they will give discount on the two rear tyre pitty I must fit Pirelli again otherwise I must buy 4 new tyres. Pirelli SWAK.