I can't buy base game because of a bug

Buy it as a gift and activate from your inventory.

are you sure you cant get the regular coh2? COH2 oberkommando is a stand alone game( that oddly can be dlc too) just so you know. it doesn't necessarily require coh2 to play. but as for not being able to buy coh2 im out of ideas, i guess contact steam support if it doesnt fix itself in the near future

Did You get the CoH 2 Multiplayer key from AlienwareArena? Then yes, it says it.

"Tragedy" indeed: woe is you.

technically, what you have is not a DLC.. It's a stand alone game giving you access to multiplayer gaming.

Follow these steps. It's from one of their guys.
http://steamcommunity.com/app/231430/discussions/3/540742667942898736/

I got the standalone multiplayer from Alienware and as such was recognised as owning the game but never actually tried buying it. As well as the previous suggestion to buy as a gift redeeming a retail key should also work - at least I was able to withoutissue.

According to this article, you should still be able to buy the game.

If you purchase Company of Heroes 2 - The Western Front Armies before purchasing Company of Heroes 2, you may notice that the Steam Store tells you that you already own Company of Heroes 2. This is because the games share many assets and launch from the same Steam Library entry.

The Steam Store ownership check can be ignored in this case - you can still add Company of Heroes 2 to your cart and purchase it for yourself. This will add the standard Company of Heroes 2 content to your Steam account.