Totally dissatisfied with the service

Greetings all. I just cannot believe that one can receive such poor service from a mercedes benz dealership. My vito panel van was in about 4 months ago because it failed to start due to the complete ignition system being dead. Had the whole ignition system replaced and new key coded. Also complained about engine light coming on. Differential sensor was changed. All this done on my cost. About a month ago the VItos ignition system failed again and engine light started lighting up again. Another key was ordered and I was told that that oxygen sensor needs replacing and must be ordered. I then asked for Vito to be serviced while it was there. I took delivery of vito only to find that it had a oil leak that was not there before. The back brakes was replaced but the hand brake was not even adjusted. I complained to the manager and they sorted the oil leak and brakes. About 2 weeks ago i towed vito for diesel leak. I was told the mounting bolts on pump broke and had to be drilled and new pump installed. I was later informed the old pump will be put back. I took delivery of vito only to find that the engine light is on and the vito has a noise by the engine which was not there before.