My life sentence with MTN

I have multiple contracts with MTN and one of these have been for a number used by someone I don’t know( they made a number error when setting up my son’s phone contract) and after more than 4 years and visits to multiple MTN shop’s, multiple e-mails, multiple phone call’s etc I’m still paying for that phone number. I now finally had enough and gave notice but when I started to find out about transferring all my numbers no notice has been put in place. It feels like I’m stuck on Groundhog day paying someone’s phone bills till the day I die.