Broken Promises and in my opinion Thieves.

I sold my car to them and they stated they will settle my installment at the bank a month later my vehicle is still not settled, they paid over R50 000 to MFC but there is still over R100 000 outstanding every time I follow up there is some sort of an excuse, like cash flow or not its, has been done they will follow up. How do you operate? worst is I have a Cartrack unit in the vehicle I sold to them which is still legally mine as it is still registered to my name since they have not settled and re-registered the vehicle. they have been driving around with it each day as I can still see the trip reports. I have now no other option but to get my attorney involved to get this mess sorted out and I will go fetch my vehicle today as well