This might not be correct but apparently the customers claimed a chargeback on flights that they declined to take due to FCO advice but the Ryanair flights actually operated. To Ryanair these customers were "No Shows" and were not entitled to a refund, the customers should have gone to their travel insurance supplier and claimed on that but they went straight to the card supplier for a chargeback. If this is true and it's a big if ? then the customers have fraudulently instigated a chargeback as Ryanair supplied the service for which they were contracted but the customer declined to use.