FNB giving me overdraft without my concern

I’m very disappointed with FNB ,I reported unsuspicious messages that I received in my banking app regarding applying for an overdraft of 18500 and new card being issued.I was contacted by one of the consultant who told me my profile does not show any new application … three days after the phone call I received another one saying they apologies the overdraft will be now 11000 … all this are happening on my profile and I did not apply for any overdraft. Yesterday I wake up to a 11 000 overdraft ,when I try to rectify this with them and prevent who ever from using money through my name …FNB just put me through to different consultants who were in able to help …let me put you through to this …it’s like their not even sure which department handles what type of queries I really felt sad and frustrated because no one was willing to help …if really this is crime they could have prevented the matter before it could actually happen.I had to Google to check how I can remove this overdraft facility on my account before I have negative I know nothing about …I managed to reduce it to 1 but I’m really scared if FNB could not pick this activity on my profile how did it happen and what else is happening at the background that one does not know about …even I cancel all my accounts with then application can still be fine and find myself with debts I know nothing about .please share if you have experienced this with other banks