MTN failed to reverse upgrade and i'm paying the price.

In November 2023 I took an upgrade for one of my numbers and i was given a 10 days cooling off period if i decide to cancel/reverse the upgrade, before the ten days finished i decided to call MTN customer service to reverse the upgrade. And i was assured that the upgrade cancellation has be done. To my surprised when i received my new invoice and i see that i was billed for the upgrade, and when i call MTN to query, i was told the upgrade cancellation was put on the system but it then cancelled again by the retention department. and when i was transferred to the retention dept, i was then sent to another section. long story short, no one could explain to as why wasn't processed as it was logged. i called many times and get the same treatment got sent in between departments with no answers or solution. at some point i asked to speak to somebody in charged and i given to the supervisor who also could never explain to me what happened, he then asked me to give him 72hrs to find out and he promised to call me back, till to date i never had from him. its been a month now and MTN hasnt sorted the issue out and the upgrade is still active i am being billed again for the upgrade that shouldve been cancelled. to top it all when i requested all the recorded call i was told that i can only get records from customer services only not from all the other department that i was sent back and forth to. but one mtn agent told me that each department keeps their own calls record. So why does MTN is lying to me. is it because they covering up for the mistake made by one of their own? and they suspended my lines because i refuse to pay for something i didnt want. so i want to know from the management, is this how a big business like MTN treat customers by forcing them into contracts they don't want? so who is taking accountability for all the stress and the inconvenience they caused me? I want answers and i want this is issued sorted.