I bought entrenchment from stardock, and i cant download it.
Are you sure about that? All of the links on the Sins website and Stardock Store for Entrenchment and Diplomacy route to GameStop/Impulse. You also need to have previously bought or registered the base game with Impulse, or with us prior to a year ago, in order for it to appear there.
Double check whether the purchase receipt says it is from Stardock or GameStop/Impulse. If the former, contact [email protected], if the latter, contact [email protected].