Incorrect billing and non service

My WIFI was due for upgrade 26 Dec 2023, but MTN discontinued the package, so I went to an MTN store in Mmabatho for advise, I was advised to upgrade to a phone on the same wifi, which I did on 22nd December 2023 in MTN branch in Welkom. The upgrade was approved and I received the iPhone in January 2024. MTN claim I called 29th December to cancel which does not make sense as my upgrade was successful and I asked them to listen to the recording a month back and they never got back to me because they know there can never be a cancelation if upgrade was successful. I am not paying the R14k of cancelation because there was never one requested. Remember you discontinued your product that I was more than happy to continue with now your incompetence must cost me afte 10 years of being a loyal customer.