Fix or refund?

Hey, I just purchased the D3 DLCs thinking that I could use them via D3:A. I’ve installed them and they do not seem to work in game. I’d like some advice on what to do to ge them working, or how to get a refund. I purchased D3:A through Steam, but the DLC through the Positech site. I’m having no other problems with the game. I would really like to have the DLC content, but I have zero interest in buying the D3 base game. Is there anything I can do? If not, how to I go about getting a refund? Thanks.