Billing me for a line I do not use

I cancelled my Telkom line September 2017, received confirmation of cancellation and was even contacted as to why I am cancelling. We moved house and the speeds that were available (2mbps) was not sufficient so I proceeded with cancellation. In January I received a bill for the line I cancelled! I called to inquire and was asked to forward cancellation letter through again. Nothing happened. I received a bill end of February again and also the end of March. I have sent through 2 more cancellation forms but no one comes back to me and the bill just keeps growing. We moved in the new house 1st October and that line was never used again but yet I am being billed for it!