Cancellation issues

On the 12th of March I went into an MTN branch to move my contract to a prepaid account as the contract period was over. I was helped and went through the cancellation process, I was informed the change would be immediate, I received and MTN SMS stating the same. However I noticed on the MTN app that I had a bill incoming for the second month after cancelling. I have tried to call the helpline(135) multiple times, each time getting bombarded with ads while I wait over 30 minutes for a call to be answered. Twice the call was "answered" only for the line to go dead and having to restart the call and listen to the same useless ads on repeat. I did eventually get through to a consultant who informed me the line was actually on a month to month contract (even though the SMS MTN sent me on the 12th of March stated outright cancellation). The consultant then transferred me to a different department only for the line to go dead and requiring me to go through the insane wait again. How can a cell service provider have worse connection quality than anyone else? I want this line and bill cancelled and moved to a prepaid number as was promised over a month ago.