Terrible after sales service

I bought a second hand car from this dealership @Mercedes Benz East Rand (Cnr Rietfontein & northrand Rd, Boksburg). After 10 months or so of driving the car, I was notified, by another dealer, that my car was showing signs of defective paint work. I've never been in an accident and thus have never taken my car to be painted. I went to them, @Mercedes-Benz East rand, to show them the car, which they did including the manager. He personally went out to see the car. Then they said they would get back to me (mind you I drove all they way from limpopo). Today they are telling me the manager wants to see the car again. It seems they now think I am the one that damaged the car. It seems I'm being given the run around, because they are asking me to come back all the way from limpopo to the east rand to show them my car (again) which I have already shown to them. Meaning this exercise is costing me way more than it should for a fault that isn't mine, a fault that wasn't disclosed to me at the sale of the car.