Unprofessional Service

I took my car to Mercedes Cargo Klerksdorp for engine light fault and also the car was Jerking after I drove 50km. My car was about 2000km due before service. They did service A and Exhaust as a results of solving engine light. I paid a heavy amount of money, same day I pick up my car, The engine light came back and car start jerking again. The car was return to them, and they say engine is stuffed and complete engine need to be replaced. They phone me the following day with report that my engine is Ok and the starter is the problem. I argue the findings and they insisted that I must pay for the starter apx (R15345.00). Ok new starter was installed still the problem remains. 6 weeks of horror for Cargo not knowing what they are doing. I am waiting in anticipation for the good working part that I need to replace at my own cost.