Cancellation - but still receive threads

I've cancelled my Telkom account (including 4 lines) with Telkom in 20 July 2015. I received my last bill (so I thought) in August which we have paid. I did not receive any more bills which I then assumed all were cancelled. Then in November the SMS of outstanding amount. Then on 14 December 2015, another one, where the amount is suddenly double and I get threaten with Attorneys and Black listing. <br> <br> I run a business and cannot afford to be black listed. I think of cancelling all my other business and residential lines and make use of another supplier.