FNB share bank details with 3rd party without your approval.

FNB is sharing my bank account details with a third party without my approval. I took over a business in June 2019. During our visit to the FNB branch, we updated the account, and the previous owner was removed, or so we thought. However, the ***** department confirmed that the previous bank owner still had access and has taken money out of the account without my approval. So, how secure is our data with FNB? Now, I need to waste my time getting new bank account logins and visiting the branch, spending more than 4 hours to get this updated, just because FNB did not do their job 4 years ago. If this happens to me, how many other people's information is still shared outside?