Unauthorised debit order

I have been a Discovery Health member for years, a few years ago I decided to cancel the membership due to financial reasons I was sent a cancellation letter showing that my membership was cancelled. Years later they decided to do unauthorised debit orders, meaning I didn’t give them authorising to debit my account. Tried stopping it with my bank but failed as the bank said it’s not a normal debit order. This has been happening for months also messing up my account with my bank. A lady called me 2 weeks ago saying she will stop the debit claiming I used my account after it was cancelled, which doesn’t make any sense. I pleaded with her to cancel the unauthorised debit order. An unauthorised debit order took place again this morning can someone help please please help me