I had the very same thing. In my benefits page no option was visible where I could order the filters. I then contacted Leica directly by email. The answer I received was quick but discomforting, to say the least. Leica told me they only send the free filters once for any single M8. My camera serial number had been added to their database in September of 2007.
I bought my M8 new (according to the camera store), however, last December of 2008. So either my M8 was previously owned and the store resold it as new, or some camera stores try to win a quick buck by ordering Leica-filters for yet unsold camera's. Alternatively, there could be a problem with Leica's database were the system lets people order free filters based on guessed serial numbera, rendering the option for the real camera owner impossible.
What bugs me most, though is that Leica told me my M8 was registered by someone in Amsterdam, which is too much of coincidence because that is where I bought it.
Cheers, Maurits