What Mi7ch said...
What you are seeing is likely older messages that did not send the actual invite but you are seeing the Accept/Decline buttons anyways. I'll push a fix for this which should clean that up.
Edit: I spoke too soon. If you are seeing the Accept Invite and Decline buttons then this player has sent you a Clan invite. Unless you explicitly "Accept" the invite they should not be showing up as a Chieftain/Captain/Mobster/Squad. Just decline the ones you don't want to clear this out.
Last edited: Sep 24, 2015