Adding insult to injury

So I had my rear brake pads replaced @ tire mart Randburg yesterday. On my way home I heard a terrible noise coming from the back wheels. I stopped, fortunately, as I found that the left back wheel was completely loose, missing one wheel nut. If I did not stop I would have had thousands of rand worth of damage or probably would have caused an accident. This morning I phoned, not to ask them to fix their mistake but merely to tell them that I was not happy and that I will not be returning. I was told that it must have been someone at the office that loosened my wheel as they can see on the camera that it was tightened. Imagine that! I park in a secure ba*****t with 24 hour security that know my car, I have been parking it in the secure ba*****t for almost 2 years now, never an issue. I had my car with tire mart once and there is an issue. The only people that worked on my car was tire mart Randburg. All I wanted was a sorry for what happened and to maybe stop it from happening to someone else but instead I got insulted. I was not planning on going back and will not go back to tire mart Randburg ever again and I will make it my mission to tell everyone what happened. Be careful who you trust with your car.