even if you don't have an Air France/Flying Blue account, you should have received an email of the kind below, with your voucher included as a .pdf with details of how to use it.

Note that, unless your flight was actually cancelled by the airline, I don't think the voucher would have become refundable but would have had to have been redeemed on a new flight. If you voluntarily cancelled the ticket yourself, then the voucher would have lost its value 12 months after being issued if not used on the Air France website to book a new ticket.