contract cancellation

My contract with mtn is ending on the 28th may 2015.i have been calling their call centre 808 to ensure that the contract is terminated but I get transferred and put on hold for more than 30 minutes.i have tried 3 times already and still no help.if I don't call to cancel the contract, money will still be debited even though the contract is ending.and I know that if I was upgrading my phone, the consultant would have contacted me within a day