Trying to cancel my contract

I have been trying to cancel my father in law's land-line contract with Telkom for 3 months but here I am today with yet another bank statement saying I owe them money as if I've never tried terminating my account with them.

I contacted Telkom in April and informed them I'd like to cancel my contract with them, I filled in the necessary forms and I was told within 2 months my contract with them will be terminated. I figured for sure everything was said and done until I received a statement for the month May stating I owe them money, I called once again and was told the amount would be reversed and I would receive my deposit back. Then I get another statement for June, turns out the amount wasn't reversed from the month before and was apparently still to be reversed. All the times I've called they always say I'll be called back to confirm the cancellation but no one ever does I always have to call them and question them if they've got the job done. I honestly am livid up to this point, I mean I don't have time to be calling people telling them how to do their job.

Today, the month of July in my hand is yet another statement this time apparently I owe a different amount - I called earlier today and found out that only half of the amount I supposedly owe them was reversed, I fail to understand how or why -this is getting absolutely ridiculous I can't be dealing with the same nonsense every I just want to be totally done with Telkom I have not even got my deposit back I mean seriously what am I supposed to do??