Hello, my name is Mark and I will try help you with this.
What you have been told by the warranty company is standard practise.
The warranty isn't actually a warranty. It is an insurance policy and normal wear and tear is not usually covered.
As for what is normal wear and tear, that is more difficult to define. You will probably find that if it is determined to be normal wear then it wasn't you that caused it. The previous owner might have abused it.
What I would suggest though is if it is wear and tear then you ask the garage you bought it from to cover the repair costs as the wear must have been present when you bought the car.