Can they rectify their mistake - doesn't look like it....

I have been a customer for more than 30 years - no issue until last year. Someone did a ********** upgrade on my account in May 2020. I mailed in all the documents and Vodacom agreed even paid me some of the money back and changed my contract back to the original, all good BUT they cannot remove the handset payment from my account. I have been calling different call centres for more than a year with promises and redirects but no resolution, and every month I pay for a handset I never bought and don't own. Unfortunately the customer service call centres and even the Vodacom shops cannot help and there is no way of getting past the call centres. I have no idea what to do, go to the small claims court? I don't want to change to another provider and don't want to change my number.....