Long time ago a friend and me once submitted a whitehat bug that allowed the user to send messages to anyone even if they disabled messages from non-friends, i don't think this option still exists but anyways Facebook told us this wasn't a bug, we didn't even argue, suckers! i now wish i did the Same as Khalil and recorded the bug.
Well, if you have the email, just reply to it and re-open the conversation and see what happens. If you can explain it correctly, they might be able to research if the bug indeed existed and was fixed. I did a follow up on a bug that I submitted before the whitehat program was in place and that I never got a response on. They looked up the bug, replied to me and paid me. Very diligent.
