Debit NGO bank account with Greenback fees without autorisation

I am the accountant for an NGO.

On 5 November Nedbank debited our account with "Greenback Greenback Linkage Fees" - at no stage was this authorized by any of the signatories. Not able to make an appointment with our "Branch" online - Which I was at yesterday and it took me an hour just to get inside due to the Covid que. Apparently some customers are more important than others as "general public" was made waiting while "commercial" customers was let in quickly. If you confront them, they get rude.

So a NGO cheque account gets debited without authorization - can't make a booking for an appointment, cannot be helped by the call center - I am presuming that they are hoping I wont go into the branch so that they can get away with it. What hope do I have that they will actually assist me in the bank?????