Cancellation of the contract

I have been using mtn for the last 16 years.. Now I want to cancel my contract with them.. I'm being thrown from pillar to post with lots fo reference numbers.. And still I'm getting billed just spoke to Athule with no luck terrible service. Can anyone tell me how to cancel it as I have followed all the protocols by calling them a month before now I went to the store and they tell me I was supposed to cancel it 5 days ago here is my reference number ***