GoKarts USA shipped wrong part, won't respond Pleasant Hill, California

I ordered a go kart/dune buggy from GoKarts USA. We also ordered an upgraded exhaust muffler system to go with the buggy. The buggy arrived okay. The muffler system was not the one ordered or one that even fits the buggy. The item should have been a Turbo Kit GMAX, but instead we got a Turbo Kit Double XX. The bends in the pipe do not even allow installation. I went to their web site and entered the issue and got no reply. I did this three times and also started calling. They rarely answer their phone and you just get disconnected. I got through a couple of times. One time the lady answering the phone said someone would call. No one did. Next time she said the right people were out, but when I complained she gave me to Mike. Mike promised to call the following Monday. He never has (over 2 weeks). Next time the lady said Mike was busy in a convention of some sort that week. She promised to call me back the next Monday, and that was three days ago. Don't do business with this company. The exhaust system costs around $400 and I'm going to have to work through my credit card company. I also had a small problem with the fuel valve, and of course they have not responded to that.