Stripping car part (extremely disappointing)

On the 14th January 2016, i took my car for a service to this garage and my car was working fine, the only thing that need to be fixed or cleared up was the air bag, all BMW do give you a indication on what might be wrong with the car, as mine did. when i left my car there and i thought i left it to a capable hands, i got a call from Marcus telling me he has done the diagnosis to my car and that will cost me R750 that where i started it all started.<br> so i question him, everytime i book my car for service i have to pay for a diagnosis, he said it depends on the faulty of the car. but mine i knew what was wrong with it, i even mention in it to him. the air bag need to be re-setted. he then told me he picked up some more faulty in my car, and yet the car never indicated, obviously this guys want me to pay for something i do not know about. he said the car has a wrong batter, this is not the origional battery , now my question is, who replaced the battery. The price went up to R7000 when i got there to pick up my car as he phone , and tell me my car is ready i must come and pick it up. when i got there the price went up, and my car was not starting anymore completly broken.