Fnb taking long to investigate *****lant activities on my account and threatening legal action against me.

I am an account holder with fnb and had my card ****** on the 2nd of September, my account balance at the time was 000 so I just canceled my card and didnt go to the bank to get another card. On the 11th of September I receive notifications that money is going out of my account and I knew immediately it was the overdraft since I had no funds in my account, I went ahead and reported ***** on the transaction. Then this carried on and I went to the bank and reported the issue and was told a ***** investigation case was opened. The payments where being made on toll gates along N1 and was told to expect a cal from the ***** department which upto now hasn't came thru. However I am very frustrated because the bank keeps calling me to deposit funds into my account and threaten legal action against me as wel as closure on my account. I would like to take this further but j have no idea what channels to follow as i feel the bank didn't do enough to protect my account. Funds where utelised on the 4th and the 5th of September but I only recieved sms notifications weeks after. Surely had I received the first notification in time my account balance wouldn't be on negative.