Purchasing Heavensward help

So my mog station account is really old. Original beta test access n whatnot. Recently bought the game on Steam, bought the DLC. DLC code is invalid when registering.

Check square's web page for normal purchase, and of course the PC version is incompatible with Steam version... Yay technology.

So, to sum up, PC version incompatible with Steam version.
Steam version incompatible with my mog station account.

I just wanna throw 40 dollars at Square so I can do stuff after level 50... Am I asking too much?

They don't care. Don't use more than 2 hours playing FFXIV on Steam or they won't refund you either. It happened to me.