poorest service ever

I have a problem with a car that I bought from Motus Renault Zambezi. I bought a Renault triber 1.0 prestige 2022 model last year August from the dealer. Since buying the car the gearbox has been giving me problems. I took it back 4 times already in which they continuously told me that there is nothing wrong with the car. the car sometimes selects gears and other times it does not want to. On Monday 13th November 2023 I took the car to Renault Centurion for her annual service and for a second opinion on the cars gearbox. They said that they would recommend that the gearbox must be removed for a proper investigation and that it might be a clutch problem. On 14th November 2023 I took the car back to Motus Renault Zambezi where I bought the car and told them what was recommended by Renault Centurion they told me that I must pay for the work and that they are not liable for any damage to the gearbox. I have emails between me, Renault SA and the dealership where they were instructed to remove the gearbox for a full investigation, and it was not done. That was supposed to be done on the 4th time that I took it back and they booked the car in by them for a week. Now that the warranty on the gearbox is over and someone else might know what the problem is they told me that I must pay as the warranty on the gearbox is over and that they will not work on the car before any payments are paid by me. I told them that the problem occurred long before and that they can’t hold me liable for the damage as I have already told them on 4 occasions that the gearbox is faulty.