Pathetic customer service

I bought a second hand Ford Focus at Williams Hunt The Glen I was assisted by Mfundo Williams, few months later an a ngine light popped up I informed the dealership to cut the story short they couldn't fix the problem and I opted for the exchange of goods in January 2021 now my problem is since January I have not received the disc and registration papers since the vehicle was purchased cash, I have tried countless times to remind Mfundo Williams but he always makes empty promises, I am fed up as I don't get any feedback from him if I don't call him, I have been going to his office but he always has excuses. The disc expired on 31 March 2021 he gave me a temporary permit now it has also expired I am really tired of waisting my petrol running after him I don't know what to do anymore. His customer service is pathetic