Substandard workmanship

I have purchased a vehicle secondhand from them in April 2025. There was a problem with the gearbox. I took it back to be repaired and waited more than a month. When i got it back it was not fixed properly. They fetched the vehicle and did replaced the mountings. The gearbox has still issues. I can't get the warrenty from them and I believe the people fixing the gearbox did not do a proper job. There own workshop I believe is also not up to standards because the first time I took it to them , they told me a lot of bs about the computer that needs to be reset. I went to an independent gearbox expert before I took the car to them and they confirmed they gearbox was faulty.