FNB Demand Deposit??

I received a notification at 11pm on 22-06-2022 stating that my account is overdrawn. when i checked further there was a demand deposit on my account for R650.00. I did not authorize this debit and when I queried this with FNB I was told that i will need to log a dispute which will take 7 - 14 business to resolve. Please look into this ASAP