So, i read all my private messages etc+ social group invitations, and it still shows that I have a notification. I keep on clicking the group inv, but it is still there. Any help?

Try logging out and then back in to read the messages. You could also try marking them as read. Hopefully this will work.

Oh, trust me, I've done that numerous times. Doesn't work. Thanks for the advice though.

Decline the invitation.

you must go to private messages>social group invitations and there enter the invitation and click on Join or decline.