Bad workmanship

I took my vw kombi in for a few minor repairs. After 6 weeks of phoning and going in to the workshop. There was always a new problem everytime we phoned or went in. They never asked permission for any of the repairs. But they eventually rebuild my cars engine without my permission. They are now suing me for R 20 000. After which the cars engine seized and i've had to have it rebuild by other mechanic which cost me R28 000.00. They messed the gearbox up completely and I will need to have it replaced at another R11 000. They did the same with my husbands merc. Told my husband it wont be more than R15 000. Only to receive an invoice for R30 000 and the car is still not right. Still got the same problems, after the car being there for 8 mnth. When you confront them they become rude. Never signed a job card or gave permission. They don't know what they doing. I'm not going to leave this matter here. How can they just rebuild your engine without your permission. Ronnie never phones you back and the different mechanics give you different info. When you confront Ronnie he denies it all. After I told him that if there is major things to first ask me as I don't have R30 000 again.