Paint problems of the 2006 Chevrolet HHR

My 2006 Chevrolet Hhr is getting sandblasted on the rear rocker panels over the course of normal driving down paved roads. The car is equipped with protective plastic guards which are taking all the abuse. I was told by the dealer this is what the guards were for. Finally they took pictures and decided to repaint them and install mudflaps at their cost. Now the paint is still getting sandblasted again and the paint is peeling off. After complaining yet again I was told by the gm business resource center that I should have purchased the runningboards at the time I purchased the vehicle if I wanted to prevent this from happening. How was I to foresee this problem? they refused to install them at their cost which I believe they should have. They are saying that I am picking up 'road debris" and that's the problem. I only drive on paved roads so this is a ridiculous and false statement. Finally today they called and agreed to pay for 50% of the runningboards and the installation of them. I do not have the money to compensate them for an obvious design flaw. There is no reason that this should in any way be my responsibility.