Have a question (contains spoilers)

Ok so I know that the guy in the end that they tortured was not the character Bill played. So during the whole torture scenes, who was it that they tortured (as in which actor played the role)? Am a huge fan of Bill and only watched the movie because of him and I feel somewhat cheated. :S There were times when I couldn't really recognize the guy being tortured (before the reveal) but I assumed it was just the scars, now I'm not convinced. I'm still sure it could go either way because not 'torturing' Bill would have given too much away especially for die-hard fans who'd recognize him in an instant. (I have sadly failed there...perhaps if I rewatched it...) So anyway, anyone have any ideas?