Seatbelt malfunction cannot be repaired

My car a 2013 Mercedes benz C180 be Coupe has had repeated problems with the seat belt mechanism. The seat belt is one of the most important safety features in a vehicle. The belt was replaced once however the problem persists.My car was at Mercedes Benz Umhlanga for 5 days now and they still haven't repaired the car or provided me with a courtesy car. I am stranded during the holiday and have not been able to take my holiday to JHB with my family. Another problem is that my vehicle was taken on a joy ride by Mercedes Benz Umhlanga staff into Kwa Mashu and driven at reckless speeds of Between 160-180 km/hr by the service department staff while running personal errands with my vehicle. The staff member was caught when I reviewed the detailed tracker report on my car. This is disgusting service at its height. I was also told by my service advisor that this is how Mercedes South Africa operates and if I am not happy I must change my brand...! Disgusting!!! I have been advised not to touch the car as if the seat belts malfunction mine and my sons life is at risk. I have pics of the seatbelts not retracting in the dealership I was told it will be replaced yet still nothing!!!!