Account closure not processed

I called Telkom to cancel my contract because they were deducting a lot of money every month on my account, when I canceled the contract they told me they will deduct a certain amount month end, what is due including breaching the contract, we agreed, come month end they did not deduct that amount, I called them back and asked why, the lady said that's the amount we are deducting, I said so does it mean that's all and I don't owe you, she said yes I said very if the account is closed, se said its closed and indeed it is closed because I no longer get data and airtime, however I received a statement for December saying they'll deduct a certain amount, of which I don't know what it's for. Telkom is really annoying me and I will not pay that amount, if they can deduct it I'll reverse it.