Honestly...
Why dont you just hire a professional security expert for helping you? If you have that many follwoers and that high financial risk, it would definetly be worth it, and won't take him more than two hours (including consulting for future security) to figure this out.
That wouldn't help us. We found out that facebook removes our followers due to "Underage Fan Removal". This is the case because the hacker postet pornographic pictures. So we got control over the page now but the "Underage Fan Removal" is still removing many many of our followers.