Bad Service

Our car has been service at Mercedes-Benz WBS in Pretoria. We did request to replace the windscreen as well. After a week we have to.make several calls to ask about the process. They always say we will call you back but never did. Today we attend a wedding in Utrecht and after the service in Utrecht it start raining, when my husband turn on the wipers we just hear a bang and see that the whipers got twisted. We did stop and notice the nut was not tighten. We then phone Mercedes-Benz SA no one knows where Utrecht is. We phone then all te garages nearby. They assist us but now we have to pay the bill for a car that is still under warranty (34000km) and we miss the reception. We were busy ordering a new Mercedes-Benz but after this I don't think we will continue