Can change banking details

I've been trying to change my banking details since November, still no help from MTN. I have phoned them, I've tried e-mailing and went to our local MTN. Still nothing the bank account you are deducting from will be closed end of the month so don't come and ask me where is your money come the end of January 2024. So either get someone who can assist me in changing my banking or cancel my contract so that I can go to a new service provider.