No customer service

I have had an outstanding card authorization reflecting on my account for over a month and have tried to resolve via a branch, secure chat and email however keep being told that there is nothing outstanding showing on their system. I know this because the is no debit, credit or Merchant transactions for this amount on my account and i have no idea why fnb is reserving the funds. As a result my account goes into negative and i am charged the overdraft fee as well as item paid, no funds available fee as a result of this hold on the funds. How am i supposed to resolve this when noone gets back to me or knows how to resolve the issue. Truly contemplating just moving banks, what horrible service fnb