Sucking money over a contract that should be cancelled a while ago

I have a cellphone contract with Mtn and wanted to cancel the contract and i was told to pay an amount of R 2050 which I paid and requested a settlement letter and I received the settlement letter but the contract was never cancelled, to this day I keep getting emails with an invoice attached to settle, each time i get these emails I send emails enquiring why am I getting an invoice to settle when i requested for the contract to be cancelled and no body ever responds to my emails. When I call them to speak to a consultant their answering machine never gives an option to transfer the call to a consultant. . I don't understand why would you send me a settlement letter which proves that I paid what was due to you and yet bill me for an account that was settled, this contract should be cancelled by now but I'm busy going back and forth over one thing that I never get an explanation on . Can someone at MTN get to the bottom of this urgently and cancel the contract. I am so frustrated with the service at MTN, this is no way to treat customers. Each time I write an email to you feels like am writing to a wall that will definitely not respond. I really need this contract to be cancelled and stop sucking me money that I don't have