Billing for expired contract

I reached my 24 month subscription period with MTN two months ago (March 2015).<br> I called them a month before the end of the 24 month period to notify them that I did not wish to extend my subscription period and I was requested to call a few days before their billing date. I called them again as requested and I was advised that my subscription would be terminated. That was 2 months ago, they haven't cancelled my subscription and continue to bill me for the subscription. I have called them again and even been to one of the stores where I completed forms to have the subscription cancelled and the number migrated to prepaid. But the subscription has still not been cancelled.<br> Below references for my calls to MTN:<br> Ref ***<br> Ref ***<br> Ref ***<br> <br> Please assist in having MTN canceling my subscription and migrating my number to prepaid.<br> Thanks<br>