Service disaster

I bought a new Mercedes Benz C280 in 2008 and have had it serviced regularly (first under motorplan, and then paid by me) at Mercedes Benz Bedfordview. Because of my low mileage (85000km) and extra specs (AMG, Harmon Kardon sound system etc) I have had no inclination to replace it. I booked a service on Thursday 29th July, and was telephoned by my service advisor (Lappies) at about 10h00 to say the car needed nothing other than the usual service, and quoted me R5300. I fetched the car at 16h00 and paid the service fee. On driving out the gate of Mercedes Benz, several warning lights came on including one indicating that power steering was faulty, and I felt this immediately. I drove back in, and the car was put on a lift, examined and attached to a computer. I was then told that a unit that governed several modes (including braking and power steering) had to be replaced at a cost of R33,000 and the car is now unsafe to drive. Nobody could explain to me how a car that was driven in that morning in perfect working order could be serviced and was now unfit to drive and would cost me R33000 to repair. The car is still there, where a subsequent examination on Friday 30th could uncover no reason for this failure. Despite messages left for the dealer principal to telephone me to discuss this, he has failed to do so. Communication to me from Mercedes Benz has been poor and briefly from a lady called Megan and the service advisor Lappies basically informing me that if I want the car repaired, I would have to pay R33000 for the part. Their attitude on the phone appears to be of embarrassment and not quite knowing what to say. I have lodged a complaint with Mercedes Benz South Africa (case number 1-**********7, case manager David Kgasoane) on 2nd August. I would appreciate it if you could take this matter up and attempt a resolution that will not cost me R33000.