Mercedes Sandton takes advantage of their customers

I was made to pay for a diagnosis when I was not informed prior that there may be added charges. When I signed the job card - I did not sign across the 3 different options provided should there be additional work to be done and the agent did not discuss this at all. When I was called to tell me my car is still being checked they did not mention that there may be additional costs included. Should I have known, I would have collected my car and not proceeded. In addition, the other clock issue I had was also not fixed and they said it is fixed. I feel that I have been misled and taken advantage of.