I want my money back

I brought my Jetta TSI silver greay at Master Gearbox in East London early this year 2019 around at February and Got it back in April having a problem with Megatronix. It did not change gears. After 2 days after I recieved my my car back it had the same proplem. I took it back and they said its still adjusting itself. After 3 months that is last July it had the same problem, I took it back to them and they said they are going to change the megatronix. I waited and sometimes called them and they said they are still waiting. End August I went to them to enquire about the amount of time I waited booom they said the car is done, I requested the paper work for the exchange of megatronix as a proof and they said they cant give me that information. They said I am still going to see the spanel on the display of the gears because I need to change the clutch.

I did a quote to change the clutch and boom again the team from Strickly VW said the my clutch if fine the only problem is Megatronix, meaning it was never changed or there was no new one installed in the first place. I called Master gearbox again and now they say I must bring a letter that is stating that the megatronix is faulty.

If there is someone to help plz assist it is frastrating and stressing because I spent close to 30k to fix this only to find that it is not fixied