Made to pay for something broken while vehicle was with the dealer

I took in my car for a throttle body change, only to be told days later that the car wouldn't start, and they had no idea why. After further more days, I was even made to st******* the tracker because they were guessing anything they could think of, of which it was not. At the end, I suspect they bridged the car somehow by installing another electronic device, and billed me more than 12 thousand include labor for something that was never a problem when I sent in the car. I also suspect a foul play by the so called technician working on the car too because over the course of solving the mess they did, arguments would get very heated. When I took my car afterwards, I noticed the gear movements were not smooth as if it has been very badly driven, probably without even using clutch and wrong gears, but unfortunately I can't prove. Also, some strange noise started on the engine, afterwards, and I recently found some debris on the engen sump as if some pieces were thrown inside the oil cap. Unfortunately I can't prove that either, but I suspect this. My main complaint that I have proof of is I took the car in for a throttle body change in Weiss Volkswagen Durban and while the car was with them, I don't know what they did, but I ended up being billed for another thing that had no problem when or before I left the car with them. I am still very angry at how this was handled and will submit a formal complaint with rmi and miosa