exact same thing happened to me, in the end activision had to kick me from the clan then re joined
If a live agent isn't available you can try via the support link at the bottom of this page, or by talking to @ATVIAssist on Twitter and they'll sort you out.
Typically clan members become "classified" following them linking/unlinking multiple game accounts to their Call of Duty profile. That's not the only reason it happens, but is the most common and it is being worked on at present.
The samething happened to me, if you find out how to get your own clan back, then please let me know. Thank you.