hey i did talk with activision yesterday. they told me to have you try 3 things.
1) clear your xbox cache (see my video you posted on for all details)
2) unlink your account on callofduty.com and re-link it
3) if you have a smart phone or ipad. download the ghost app and send a request to join the clan. you can find us under XGC MILITANT.
I will keep trying to send you the clan invite from my end. let me know if any of these things work. otherwise you will have to get a hold of activision by going to callofduty.com and click the support tab on the top of the page. then click the live chat with agent and they can help you more. let me know if you need any help with any of these steps and i will do what i can to help you.