Billed for an expired contract

I'm very frustrated as my contract was ending on the 16th of October 2022 and I did an upgrade on the 16th of October 2022. Now MTN is telling me to pay a cancellation fee of R1000. I have been trying to call MTN and they are transferring me to the Billing Department who dnt bother to pick up their phones. Can I get clarity on this matter urgently as my Credit profile is being affected