Inferior Quality Tyres

I purchased a set of tyres from Mercedes on 22 August 2016 with a car mileage of 48256. In December 2016 it was brought to my attention that the front tyres of my car were completely worn out and not roadworthy. Upon further investigation, it was noted that the alignment was not correct which led to the wear of the tyre. At this point , I had just over 5000km mileage on my car. I brought this to the dealership's attention via numerous emails and eventually got an appointment with the dealership manager Mr Ismail Essack. I was told that the wear on my car could be as a result of poor driving hence the alignment went off in 5 months. I requested further investigations on the actual tyres and was referred to Continental tyres who inspected and provided me with written confirmation that the tyres did not have a manufacture fault. I bring this matter up as at today 19 December, because I replaced the tyres in February 2017, travelled the same route as before (and did far more mileage) and 20 000km later, my tyres are in perfect condition. The question that raises in my mind is how can a brand new set of tyres from the dealership only last 5 000km and another last 20 000km and still going. My only answer is that the Mercedes dealership sold me inferior quality tyres and/or the alignment was not done properly on my car. I am disappointed with the response received from Mr Ismail Essack in that he cannot assist me further with my query. I have informed Mr Essack that I will raising the query with Continental as well as the Consumer Ombudsman.