#item paid *******

I have noticed on my cheque account that there is this #item not paid no 1 and i did not follow it up and this month again it appeared a item paid no2 with a refferenced date of which o do not understand why because i am sure that i had money before i made a transaction and there is no transaction of the money worth what has been deducted on my account. I have been with fnb all my life and was not planning to change bank but i will not allow to be ********** like this. What exactly is this #items paid things and how can you charge me if my account had funds?