Do you have status with FB? It may help to call to Paris or Amsterdam, where status may be taken into account.

Fully agree with you by the way. They took money to allow you to be able to book at a later time. Either they return that money (not being able to let you book the flight as promised), or, they should still book you for the same price (possibly on an alternative flight/service). Either they refund or provide the service that was paid for. Keeping the money and refusing the service is... unfair.