Problem with Car Care Clinic

I have sent my car for the service in Bloemfontein Car Care Clinic on May, the problem was mixing up of petrol and diesel, and when I sent my car there the engine was running and the manager who was in charge for the center he gave me the quotation of R 3438. 50 and I paid the amount and after 3 days he mentioned another problem which is the injectors and he said I must give him R16000 and I gave him as he is going to buy those Injectors somewhere, and he didn't give me invoice. And the car didn't start after putting those Injectors, he took my car to other service providers and he gave me another quotation of R34382. 40 on August and I paid the car also didn't start. Now they suspended the manager as he was ******** lot of clients. Now there is a new Manager and my car is still not running, now I want my car and my refund they refused to pay me back my money as the car is still with them and not running. Please advise how can I get assistance in this regard.