2007 GS320 Problems

I own a 2007 GS320that I love but made the mistake of putting gas in it.Called Carlton Motor Cars and had it towed there.They informed me it would take a day to fix.I called them the next day and they said it would be ready in the afternoon.Called them back in P.M. and they said they had broken a part while trying to fix the car.They further explained that it was Mercedes fault because it was(the part they broke)put on too tight.I asked for a loaner which they refused because I didn't buy the car from them,however I and my family have bought three cars from them.I bought this car from Dyer in Columbia because they had the car I wanted.After a discusion with the service manager they agreed to get a rental car. When I went to pick up the car two days later after being told it was ready,it took an hour for the dealership to process the paperwork. Today while driving to work the add coolant light came on.I stopped to check and found Carlton had not put the engine cover back on and when I returned it was sitting in the shop.Another half an hour I left but was disgusted with Carlton Motor Cars of Greenvlle,S.C.