Secret Armory

I am unable to complete the It's Like Christmas mission as someone dropped down below and glitched my game.  Therefore please if you are on this mission and have it without the glitch please let me join your game so that I can complete this mission.

Please anyone who can help me complete this mission reply to me or add me as a contact on xbl (onlyme07) so that I can complete all of the DLC for this game.