Billing nightmare

I sent this below query to MTN directly on their twitter account after i logged a query with their accounts department and still no response whatsoever. Can you please help resolve my query. i had two contracts with you, one expired and cancelled in April paid up, and the other is on going. I gave my normal notice for termination requested and it was loaded. on the 14th of April it was rightfully cancelled. notes are on your system. on the 17th of April i called in to ask if they are able to convert it to prepaid and the lady said she will make a plan to reopen the number on a prepaid. apparently it had to be opened as contract that cancelled the same day to migrate it to prepaid on your side, that was done, but the person who was suppose to cancel and migrate it thereafter forgot to action accordingly and i wasn't notified of anything regarding all this happening. I got the statement last month and i see i have been charged for a cancelled contract. How? Why? I called in to query this and i was told the query was resolved a request for credit was escalated. today i get an sms that i am owing and i know i paid. please resolve this soonest.