Selling damaged, second hand PC game with used key

I wish to make a complain about Toys R Us Heathway Square. On Saturday I purchased a whole lot of PC games. In particular there was Heros Of Might And Magic 6 Gold Edition on special for R50. Upon opening the game I noticed that the there was a slip inside the game box. Where the game had been returned due to a problem with it not finishing loading. Also the DVD disc inside is significantly scratched. I however attempted to install the game which was successful only to discover that the key code had already been used. I am extremely disappointed and disgusted that Toys R Us could still mark this game for resale under these conditions. I demand one of the two things either a brand new copy of the game or my money back for the game