Still being billed 2 months after cancelation

I cancelled my Telkom line in November after which Telkom has repeatedly sent me more bills even including higher amounts than what my normal account payments were meant to be. After stopping the first debit order they sent me an SMS to collect outstanding fees from me. I then contacted their collections department who assured me that they will not debit my account again and I will not be billed any further. Last night a debit order of R600.00 was taken from my bank account. Telkom, please get your business in order!!! This is unacceptable. Refund me the R600.00 NOW!