#Item Paid No Funds

I logged on into my app , I noticed that I had a minus of 650 on my account , of which I ddnt understand , bare in mind i dont have an overdraft acc so its just your normal current account.

I check my statements of which it details:

#Item Paid No Funds 4 Ite Ms On 25/03 for 650

of which when i googled this code it means FNB paid something on my behalf now my dilemma is that there is nothing that I owe where FNB will need to pay on my behalf since everything I had already paid and there are SMSs and emails that the payments were done and also on my statements there is proof I paid the "items" soo now Im confused why is FNB robbing me , literally daylight *******