Unproffessional and poor service

26/06/2020, I booked my vehicle in at New vaal motors for a misfiring issue, which before handing the car over I requested that a technician (Mark) test drives the car with me so that he could see and feel what the issue of the vehicle is. He noted the issue and said they would run a diagnosis which would map the actual fault of the vehicle. The vehicle was booked in, a diagnosis was done and quote was issued to me. I approved the quote on the 3rd July 2020, Total: R30 000 and they started working on the car. on the 10th July I called in to do a follow up on the status of the repair, i was told by Ruan, that theres a fault picked up, and the quote needed to be adjusted again (for plugs and a 1 coil pack), I complained as i felt that i am being misled. they discounted the new quote and sent it to me for approval. new total: R31 543.50. On 21 July 2020, Ruan called me to say the car is ready for collection, My father went on my behalf as i was at work, only to find out the car was still misfiring when he drove out, car was not tested at all (proof being my tracker log), as had it been tested, they would have picked up that the car is still misfiring, on top of tha, my car had a turbo pipe missing, yet they were prepared to give me the car as is. Ruan promised to fit in the missing pie, and the technician said the misfiring would stop once pipe installed. on 27 July 2020, i called to follow up, and was told that i need to pay R6000 more as 3 more coil plugs have suddenly went faulty, i feel disrespected and unimportant as a client. complaint was lodged with Service manager, then head office Mercedes, resolution was to discount on labour and parts. I was misled, had i known that this is how they roll, I wouldn't have given them my car! Car is still with them and Im taking all necessary measures to resolve this.. Terrible experience which was never expected from such a big brand. I regret setting foot in there.