Authorisations for cancelled transactions taking too long for FNB to release

I am not sure who is at fault here. How is it possible for FNB to hold an authorized amount for a transaction that was cancelled same day for more than a week? Even though merchant acknowledged that they are not holding transaction in their system any longer??? Transaction made and canceled same day, 03 July, and today is 11 July and FNB requested me to submit a DISPUTE..... Can someone please explain..... The reason for this review is that I just cannot get this answer from FNB. The amount shows 'pending' in my account since 3 July and this might be the only way I get FNB to address this with me. The chat system insists the merchant charged, even though after 8 days the merchant did not bank. I am sooooo frustrated with the banks and especially FNB since I hear it takes them 10 days to release a cancelled/voided transaction. I trust this comes to the attention of a supervisor or similar to have this sorted today!!