Mercedes Benz taking advantage of unsuspecting users - maintenance plan

I have received a terrible service from the Garden City Motors - Mercedes Benz Pietermaritzburg together with Mercedes-Benz South Africa. They are refusing to repair my merc which is still under maintenance plan yet they can not provide reasons for that. My car has been to the dealership for about 2 months now. I have written formal correspondences to no response. Mercedes-Benz South Africa is ran like a ****a Shop people must stop buying merc because the maintenance plan is no longer what it use used to be many years ago. I am really dissapointed on merc, I will never buy one again and I will never encourage a person to buy mercedes-benz hoping that a maintanance plan will d anything above the oil change.