You have a MW3 Premium Code?
If so... That is only for "MW3 Premium Subscriptions", Since Black Ops 2 is free for everyone you wont be able to get it. they already gave the Extention to existing mw3 premium members for all the issues they went through on Elite. The deadline for use your Premium code was Nov 12th.
I've sent you a PM with the info regarding FAQ's on Premium Memberships & Seasons Pass