I think there is some oddity on the FB website. When I first tried to logon it didn't know my name, FB number or DOB.

I decided to email them about it. There is link somewhere to email the FB service people. You click it, and it tells you you need to login to FB to do so so takes you through the same first sign up stuff.

HOWEVER this time it actually works - it has all your details correctly and you get to a form to send them an email. You can either write and tell them the website is busted, or go back to the KLM/FB homepage and login again and all should be well.

I think the link you need is Customer Support - Flying Blue - Contact the FB Service Centre then the "Send us an email" link under the Flying Blue Service centre bit.