False Represantation To Get Easy Money

On the 24th of September 2022 I took my moms car to Bosch Service Centre in Brakpan near Mall @ Carnival because it was vibrating. She said it started vibrating last month after she took it for a service around the 17th of July 2022. Went out with the driver and explained to him when the vehicle vibrates. We the got back to the store and they said they would diagnose what causes the vibrations but would charge us R1000 for the diagnostics as my mother should have taken in back within 7days. This was fair and I accepted. They then diagnosed the car and said the vibrations/shaking are caused by a faulty coil pack and they quoted me R5000 excluding the diagnostic charge of R1000. They said they would only charge R500 if I fixed the car with them of which I accepted. They said I would get the car the next morning on the 25th around 9am of which I didn't as they apparently couldn't get the parts. They eventually called on the evening on the 25th of September 2022 saying the car will be ready by 5pm. When I got there they we avoiding me test driving the car as they said they were closing and I should pay and leave. I insisted on test driving the car only to find out that the vibrations/shaking was still there and didn't get any better. I then alerted them of this and they are now telling me stories about having told my mother about the shaking when she had brought it in for service. My point is I brought in the car for the vibrations/shaking and when they quoted me they told me that this was what was causing the shaking/vibrations and I only agreed to the quote because of that. They now want me to pay for what they did to the car which had absolutely nothing to do with what I brought the car in for. They are now withholding the car because I am not willing to pay for whatever they did to the car because that is not what I brought in the car for. I was very clear that I brought the car in because of the vibrations/shaking and they went and did their own thing just to get some money in that is their problem.