Car sold without my consent or car papers

This is a classic car **** story. I am a young, female student driving around an old car. I took my car to Petrolheads for a service, and after a major service that cost R6500, I drove it away. Less than 50 kms away before the engine began overheating. I had it towed back to Petrolheads where they fixed my head gasket (supposedly) for another R10 000. Ouch. Less than 2 months later my car starts acting up again. I take it back and they say it is fine, charge me R700 and off I go again. Less than 15 kms later my car breaks down. According to Jon at Petrolheads my car is totally broken, including the cv joints, front suspension and gearbox and that it would be better if I sell it. I inform him that I understand, I can no longer afford the maintenance costs on the vehicle and ask him if he can find a buyer for me. He sold the car, without car papers, without my consent or knowledge for an undisclosed amount, fully repaired. I got a quote from a panel beater friend of mine who is fami**** with the car, that even if the car is completely broken down and undriveable he could still get R15 000. I believe that Petrolheads pulled a disgusting **** on me, and made thousands of rands.