Totally Disappointed

I have an audi Q3 currently at 28000 km, yesterday it was towed because it was making a weird sound so was advised by Audi assist to switch off and they called a breakdown. I have warranty with this car the lady i spoke to her name is Ntombi from the call centre she was very helpful she even told me it will be covered only today to get a call from Audi Pietermaritzburg that the problem is with the Spark plugs they are all damaged “assumed” its caused by the type of petrol. How is it that i had to pay for something which is not my fault and could even happen again any day so it means i have to pay again. I’m disappointed totally and need my money also I’m selling this car and never recommending buying this car to anyone. Or even going to Audi Pmb