Can't activate Fallout N.V. Ultimate Edition

[OrinOthername]

I've purchased a Fallout New Vegas physical copy a few years back. Today I was looking through the game shelf in the store and I've stumbled unto Fallout New Vegas Ultimate Edition. I got home and I tried activating the copy on steam and all I get is a message that tells me I already own the product.
Of course, my current Fallout has no DLCs. I can't use the steam key and everytime I install the game from disc it install just the basic version, because I can't enter the Ultimate Edition key ( ...steam account already owns the product...)
Has anybody ever had this problem and does anyone know how to solve it?

[Cathulhu]

Ask Support to remove your current version of the game to activate the other one.