Does not cancel expired contract.

My contract expired end of September with Mtn. After doing what they requested by letting them know 21 days before expiry date that they should migrate the number to prepaid. A day after the contract expired I phoned again to remind them. Spoke to Sumu and Montle . They promised me it would be migrated. I waited the time they advised me it would take to be migrated after that I phoned again and spoke to Leratho , Mandy and Elroy. All of them coming up with excuses as to why it has not been migrated yet. I have all the relevant reference numbers to indicate that I have indeed supp**** all information needed from me. Today my contract has not been migrated to prepaid and I refuse to pay another bill for October because I did not use the phone during this period and they did not cancel it .