Cancelled contract

My two year contract has ended, I phoned to switch my number to pre-paid as I do not want to renew my contract. <br> First call to MTN, will take 2-24 hours to switch to pre-paid. <br> Second call to MTN, will take up to 48 hours to switch. <br> Third follow up call, will take up to 14 days and apparently I should have given 15 days notice prior to my contract ending! <br> I have paid the outstanding balance and do not want to be billed for another month because MTN can not switch me over. <br>