I managed to get it working. I had to go into facebook and turn on my notifications for the game. I had them turned off. Although when I first contacted support about the issue, their automated response was to have them turned off. So I did the opposite and that seems to have worked. Hope that helps.
I'm having the same issue. On my tablet, my cell phone and on the game on my home pc. Messages shows the envelope but nothing else and I can't even click on it to open it. I've tried contacting the support people and all I got back was an email with instructions that had nothing to do with my problem. So I'm stuck.