being falsely debited

Nedbank is no longer supposed to be debiting me... I called them a few months ago about this issue and they said I did not fill in debit order cancellation forms... I than requested them they sent them and I completed them and sent them back. The next month yes I didnt get debited but the following month debit order started again...I am tired of having to reverse this every month with my bank... can they stop *****ing from me