Pick up the phone.
Numbers for Flying Blue in Belgium:
070 707 9 8
(+33 1) 58 68 68 68
This is unlikely to be something that can be quickly and easily resolved by contacting Flying Blue. Whether the agent you make contact with is aware of the problem, or not, Flying Blue is most definitely aware of the problem, at the very highest levels, given that they have apparently been in dispute with Aeroflot over the very matter for some time now. But perhaps it is worthwhile logging your displeasure at being refused lounge access, even if I suspect there is nothing very much that can be done about this in the short term.
By the way, asking a customer service representative to look at an internet forum as the basis of the explanation of your complaint is rarely a good idea.