Worst experience of my life

So I booked my car in for repairs because it was losing power, I asked the gentleman who was assisting me roughly how much are we looking at, he said around R20 000. A day later I get an email quoting me R42 000.I still asked them to proceed with the repairs. I went to fetch my car after the repairs were done, the vehicle immediately started switching off as I was driving. I went back to them twice and they insisted they just needed to tighten the terminals but the same problem persisted. The third day of taking my car in I was informed there was an issue with the alternator which I didn’t understand why it wasn’t seen when I initially took it in. I still said they must fix it which meant I needed to pay an additional R7400. A day later I’m driving on the highway the car stars smoking from front to back and it didn’t have power to a point that I almost caused an accident. I’m tying this on the side of the road, I also need to organise my own towing. How is it okay to pay almost R50 000 and I haven’t even driving this car for a day? This has to be the worst experience of my life.