Bought 2 cars cash (Almera & Opel mokka) collected Opel on the 18/08/26 @ Montana

Bought 2 cars cash (Almera & Opel mokka) collected Opel on the 18/08/26 @ Montana. On the 23/08/26 car stopped in the middle of the road without any alert. I asked my friend who's a mechanic to come and check the car and he said it's an engine failure then he removed it. How can a car have a defect when I drove +/-650 km while, Almera travelled 3 times those kilos and still fine. Shanil Daya is sending me from pillar to post, when I send what is required the response is another request after another. Ijooo bathong I didn't buy a car to be up & down with emails. Any suggestions on how can they refund me or repair the car.