False product sold to customers

I bought a Flexi cash voucher on the app I couldn't get a merchant they listed around my area, went to soshanguve mall fnb branch they were clueless about what I am talking about, called the call center i was sent from one department to another for over 4 hours, contacted them on Instagram same problem. FNB refuses to reverse my money saying it's impossible it will be on my account until I find a merchant till then that voucher will sit there On the flash site they say you can reverse the voucher but fnb has made the voucher not to be reverse