worn out lining

I have a 5 year old Mercedes C200CDI.. More than one year ago i found the lining of the seat at the drivers site is in one place worn out. I complained to Mercedes about this lack of quality. But they seem to consider this normal and do not want to do something about it. I had many cars but never had this kind of problem. Are there other people that have the same problem? So I could apply some more pressure. Thanks, Sylvain