How to unblock premium content on Black Ops 2 on the Xbox One

Thanks for trying. Let's clear your 360 storage.
Profile & system > Settings > System > Storage. On the Manage storage devices > Clear local Xbox 360 storage.

Once done, let's re-add your account from the console.
Note: Before doing these steps, please make sure that you know exactly the email address linked with your gamertag and the password to it so you can add the correct account again.

1. Remove account:
Press the Xbox button to open the guide. Select System > Settings > Account > Remove accounts. Select the account that you want to remove, and then select Remove to confirm. When you're finished, select Close.

2. Power cycle:
Press and hold Xbox's power button for 10 sec. Unplug the power supply for 30 sec. Plug it back in and turn it on again.

3. Add account:
Press the Xbox button to open the guide. Select your gamerpic in the upper-left corner of the screen, move all the way down and select Add new.

Enter the email address for the Microsoft account that you want to add, and then select Enter.

Hi there!

Sorry to hear about the issue. Let's see what we can do about that here.

Let's try to redownload your Xbox account on the Xbox 360 system. While in the backwards compatible game, press the menu and select button on your controller simultaneously to bring up the Xbox 360 guide. While in the guide, scroll down and select 'Download Profile' then enter your Xbox Live credentials.

If you have a PIN setup on your account, try to remove it first. Learn how to manage it from this link https://support.xbox.com/help/family-online-saf...

Be sure to restart your console. Press & hold the power button > select Restart console.

Unfortunately I've tried that and it didn't work I even tried on a different Xbox one where I downloaded my account and still no luck

The premium elite features for black ops 2 are free. Everyone has access to the same elite features for black ops 2

Yes, I believe that there was a one month window (which was extended by a furthur month due to errors) after the release in which you could register for a founders badge. Sorry OP, you missed that window. You can still go Premium whenever though, however
I am not sure how it will work in relation to Black Ops 2 however (like, if you go premium now, will you be able to at least get some of the inevitable Black Ops 2 DLC, or will your subscription terminate at the end of the MW3 DLC season?).