Activate Dead Space 2 on Origin

Hi,

I bought Dead Space 2 on DVD years ago. I wanted to add it to my Origin library but it tells me the code was already used. If I install it and use the license tool it says something like 3/5 installs used (probably because I had some copies not uninstalled correctly back then).

So my question is, is there a way to add Dead Space 2 to my Origin account via my product key? Why is it telling me that it has already been used?