Telkom billing mess

I cancelled my account with Telkom and under the account there were multiple lines (for a reason known only to Telkom), but when we were requesting the cancellation, we made it clear that we were changing service providers and would thus not be using Telkom any more. This in essence meant that we were cancelling the full service (at account level which should encompass all the additional lines that they had lumped up under that account number).. Now, they continued billing for months after the cancellation and they say that the other lines in the account were not cancelled (for some reason only known to Telkom!) and attempts at following up on the issue were seemingly ignored. Now Telkom has handed the account over to debt collectors who have been harassing me for the past 2 months or so. And still,I have been unsuccessful in getting to the bottom of the issue with Telkom as you speak to an agent- they say they will escalate, but nothing is actually done. I am so frustrated, but I refuse to pay an amount when I do not owe anything.