Mercedes Benz Century City - SHOCKINGLY BAD SERVICE.

SHOCKINGLY BAD SERVICE. Took my car in for a basic service (which was not cheap). Got a quote for engine fault. Took it back 2 weeks later and the quote went up with R2000. Accepted the quote after I was told that the part price went up. The car went in for the repairs. I was asked to come pay a huge deposit. Went in and paid. Was told on that day that I will get my car back in two days. Those two days plus ten more have passed. No communication from Mercedes Century City. When I eventually got feedback and had to go pay the balance, the price had gone up with another R6000. This I refuse to pay. They quoted price and then just add what they feel like? This was 3 days ago. Email them again today and copied some of the management in. Not a word from them. They still have my car...