Sandton Repo Cars sold us an unroadworthy Vehicle

Myself and my wife bought a vehicle from Sandton Repo Cars. When we went out for a test-drive they didn't allow me to drive far, their reason being insurance issues. Before buying I repeatedly asked what is wrong with the car but I did not get an answer from the owner(Mr Lawrence). We agreed on a certain price as there were a few minor repairs to be done. When my wife was driving back home the car started stalling when she had to come to complete stop. This was very strange as this was an Automatic car. I personally took it for a long drive the following day and figured that the car has 'known' gearbox problems, hence I was not allowed to drive far. We went back the following day but the garage was closed but found the garage open the next day. They refuse to listen to us and did not want to refund nor to fix the gearbox. We also found out from Mr. Lawrence that the car was in an accident but non of this was disclosed before purchasing the vehicle. Please help as they are not honest at all. Later on when we read the reviews, we saw that this is a norm from this garage. This has greatly inconvenienced us and my whole family. We were planning to start a business to support our retired mother in law. We do not have the money to fix as mechanics have quoted R25 000/R30 000. Hope you can really help with our situation.