Cedar Isle broke my car

I wish I had read all the reviews on here about BMW cedar isle before taking my car there for repairs because now they just made matters worse for me. My car is a 2016 1 series model that has never had mechanical problems and at the beginning of the year I took it in for a major service. On August 08th I realized that my coolant was leaking and decided to park the car till I can take it to BMW to get it fixed on the 10th Aug. I got a quote of 12k to fix the coolant, half of which was for labor. the problem came when I wanted to go fetch the car, when the service agent suddenly tells me there is a drivetrain error message on my car, which wasn't there when I took it in and I must pay 66k to have my turbo replaced. what stupid madness is that. I got mad and told them they won't see one more cent from and took my car. now I m stuck with a drivetrain error on my car, which wasn't there before I took in my car for repairs. I plan on lodging a formal complaint because the more I think about this the angrier I get. How do I take my car for repairs and pay so much money only for it to come out more messed up. worst service ever and I will never buy a BMW again in my life, it is simply not worth the drama when it is out of Motorplan and the service is appaling!!!