Bad service at New Vaal Motors

The service at this dealership's maintenance department is pathetic, you take your car there at your own risk. I recently took my car to Mercedes benz new vaal motors in Vereeniging for a normal service. The Service Advisor as she called herself Kershia Singh is such a noisy know it all who does not listen , so she calls and say the service was done and went well BUT your car is not having power it can not be driven so there is a valve you need to buy costing R20621 what should i do can i go ahead and order the valve...She was saying all these things sounding so arrogant as if there is something wrong i did . I told her i don't understand what she is saying since i brought a car with no malfunctions and now she is saying my car can not be driven and i told her i will come and see her the following day in the morning so she can explain. When we got there with my husband she started paging thru the job card papers and explained that before service they inspected the car and it did not have any problem but after the service they found that the car does not have power anymore and its because of a throttle valve which she says we must buy it, we told her there is no money we are going to pay all we want is my car with no malfunctions, just as on the phone she gives no one a chance to talk so she started screaming and said there is nothing she can do for us we just need to wait to see the service foreman. Waited for the foreman for more than 20min until a guy by the name of Jaques (Service Manger)came and asked who are we waiting for then we explained the problem and his response was it does not make sense we should get back the car with no faults, he took the job card papers and asked us to go and allow him to investigate and he will get back to us later in the afternoon. Later on around 10am a call comes in saying the car is ready for collection there was just a valve which was not closed IMAGINE.......what if we had told her to go ahead and order the part, I doubt she was still going to call and say sorry it was just a mistake. when we went to collect the car she was not there to explain to us.we were assisted by another rude service advisor Bianca Marx . This kind of treatment one does not expect from such a big brand. Whatever they did to resolve the problem in the car we don't even know if it is something that will give problems in future, they have given us so much doubts about their capabilities the service was BAD. Something is not done right at that service department they are either in some money generating **** reporting faults to get money from us for parts or they are using *********** technicians. Kershia Singh and Bianca Marx i highly suggest you go and do a course in customer service , ladies it will do you good-you are representing such a big brand such behaviors are unacceptable, you can also learn a thing or 2 from your colleague Linda.