Bad service

I bought a Mitsubishi asx for the lady called Cynthia in 2020 but after few days I complained about the tyres of which they replaced and after some few months there was a problem in the gearbox that I complained about and they wanted me to come to Johannesburg and I reside in mafikeng but I incurred the petrol however the problem just comes and go and every time when I tell them am told I need to bring the car in Johannesburg of which I did and the service guy drove the vehicle even the manager drove the car and felt the problem but they claimed the car only needed the tyres but the problem doesn't go away. I think they sold me the car knowing it has problems with the gearbox now they told me it's over 2 years there is nothing they can do and the 2nd hand manager left the company so I have lost.