FNB CHARGING ME FOR UNPAID DEBITS YET THE DEBIR ORDERS WENT OFF IN ACCOUNT!

I am so upset with FNB Bank!!!This is the second time that my debits go off successfully from my account,receive an email confirming that it was received successfully and then later I et an email,l stating that the debit order failed,then I'm charged for unpaid debit orders but it shows that money was available when the debits were raised,money went out of my account and then it appears to be unmet. One of these so called unmet premiums is for my funeral cover so should something happen to me I will not be covered. I want FNB to firstly reverse the unpaid fees as the debit orders where paid and ensure that the money was allocated accordingly.I am Premier client but I have to deal with this for a 2nd time this year which is unacceptable!!!.