FNB unauthorized debits

I have unauthorized debits going on my account (which I opened nearly 6 months ago). I have purposefully opened this account for my personal use and not for debit orders for better control of my finances. All my debits run on a separate account. I don’t understand how (each time) I receive a call a 031 number here are suspicious debits going off on my account. I have stopped taking calls from these 031 numbers and yet I still get debits from my account. How do these companies get my details as this account information has only been shared with my employer and no other institutions?

I have had to reverse debits from the following companies in the last two weeks alone:

REVOLVREW REVOLVR46***** (R117.50) SMART N25V***** (R120.00) KEYDIRECT 84****************** (R115.00)