Unauthorized transactions

I had a recent incident that occurred which is very disappointing because I feel our money is not safe in our accounts anymore.. I had settled an account a month ago and bank was notified about it and debit order was suppose to stop.. Somehow the debit order went off again, bare in mind Nedbank does not notify you when account is been active, no sms, nothing.. I found this out because I logged onto the app and saw.. I go into the bank to make an enquiry or to reverse the transaction and they said it cannot be done because they cannot locate the money due to account references' is not the same.. How did it get authorized is the question!!!?! As anyone experienced this and what was the outcome?