Money grabbers

I was on Topmed medical which merged with Fedhealth, I could no longer afford this so I cancelled the membership. I received an email on 15 Aug 2019 stating that the membership was cancelled. They tried to deduct money from my account on 02 Sep 2019 which is after the termination date, the debit order bounced as off course I did not leave any money for something that was cancelled. I now have to endure the bank charge of R120 for a debit order that was unsuccessful and I want it paid back. Why must I suffer for the incompetence of them not cancelling this after they send me a termination letter