That is always the first thing to do... the flight log won't help you a bit. You have to claim the miles via Flying Blue's claim system (same for all other airlines around) and they will verify the claim against the SkyTeam database. Only if they refuse and say "Oh, the pax didn't take that flight" you would need to facilitate proof. Use this link:

https://www.flyingblue.com/en/mileshub/claim/flights

You might cut it very close with the 6 months cut-off... hope it is still in time.

Calling them is useless. They will tell you to file it via the link I posted.