China rising not appearing on battlefield 4 on ps4

I bought the ps3 version of battlefield 4 with a code for china rising, always with a view of paying to upgrade it within weeks of buying a ps4, which I did at launch. I entered the code a couple of weeks ago, but before china rising was generally available, and now I've gone to play it on ps4 it is asking me to pay £12! Please help - I preordered bf4 specifically so I got access to the first expansion pack for free