Dishonest and *****ing customer,s money

I went to Bosch to get my Isuzu fixed because it had no power.i booked it in and they chaged me money for diognosing and 3 day s later they called me and told me that they know where the problem is,it is the turbo so everything will cost R12 000 and they require 50pecent of the full amount which is 6 000.i paid them the 6000 and a week later the car was not ok and they told me that I must stop calling and putting them under pressure I mst wait for their call.3 weeks later they told me that I must come and get the car.To my surprise when I get there the car still had the same problem.They said they changed the turbo but it is still doing the same and if I want it done I must give them more time so that they can arrange an auto electrician.I waited onother week.I went again and the car was still not done.They gave me the keys and told me to go to Diesel Electric because they can't get it fixed.I told them that they wasted my time and they said the is nothing they can do.They said they will take out their Turbo and put in my old one and refund me And they are very sorry.3 days later I went there and their turbo was still in the my car they refused to take it out and they didn't wanna refund me saying that that money was for that turbo.i said I don't want it because it is not working the problem is not solved,it is pointless.I didn't go to them to buy a new turbo I went there to fix the problem.They still didn't pay me even now.I don't think it is fair.I need my R6000.