SO two things if this is on your 360, you are going to want to go to your download history and download premium again. The like 160 kb file, this should activate premium in your game again and let you have access to all the stuff. Two if it somehow got unlinked from your account you will need to contact EA and have them look at it and see that you have had ...
My response from EA (copied verbatim):
no reduction is offer if you have already Back to Karkland DLC on the price of Premium is exactly the same price.
So... not the response I wanted, but at least they left me feeling warm and valued.
According to the battlefield.com upgrade offer, Premium membership is transferable and you can transfer your stats as well:
When I upgrade platforms, will my stats transfer with me?
Yes! You will be able to bring your multiplayer progress with you – your rank, score, K/D ratio, wins, time played, service stars, dog tags taken, vehicles destroyed, ...
No, you won't have premium on XBOX and will need to buy premium for your XBOX version as well. Cross-platform use of premium access is not granted; your accounts are linked (through Battlelog) but not to the point of using the same access level in both.
This has been further discussed here.