I need some suggestions

I had some work done to my car by a well known shop who I will leave nameless at this time and had some problems with them throughout the whole ordeal. When the work was finally done I had to inspect it without being able to pull it apart or even jack it up to get a better look and then sign a waiver saying they aren't responsible for damages, etc... Anyway, over the last few months I've called the shop numerous times trying to get ahold of the guy that did/ does the work but they always tell me he's not there or he can't take the call and he never calls back. Now, the work they did is causing big problems because, from what others that have checked it out are telling me, it's not done how it should have. I spent quite a bit of money and want it fixed but don't know what I should do. It's about an hour drive for me to go out there but even then I don't know if the guy will be there. What would all you do??? It's gettin to the point now where it might start breaking stuff and with that waiver I signed I won't be able to go after them for the damages.