RO2 singleplayer?

So a few months ago I bought Rising Storm. I've been having lots of fun with RO2/RS, but I just realised that there is a RO2 singleplayer campaign that is only included when you buy RO2, not RS. When I go to the RO2 storepage, it says I already own the game...



So how do I buy the singleplayer campaign? I know lots of people say that AI isn't very good, but I'd like to have this for when I'm bored and don't have internet.



Thanks.