Poor Service and absolutely no response!!!

I purchased my vehicle from GM Hatfield and have had endless issues with it. They always have excuses and do not take responsibility when they are wrong. I changed my windscreen in December and the guy showed me that the clips were damaged. I drove to GM Hatfield immediately and showed it to them and questioned them as to why these clips were damaged in the first place. They did not give me a reason. My vehicle has a FSH with them and it was purchased brand new from them. There mechanics/technicians are the only people who have worked on it. They said they would replace the clips. It is 3 weeks later and they still haven't replaced the clips. I phone on a daily basis and they do not answer their phones. I e-mail the service consultant and she does not respond! I am waiting for new tonneau cover clips from them for more than a year now. They just do not care! They do not take customer service seriously. Buying this vehicle from them was the biggest mistake I have ever made! Their service is absolutely pathetic. I will never ever buy a vehicle from GM again!