My DS wont play japanese game

My Nintendo DS (bought in america made in china ) will not play the Japanese game jump superstars for the Nintendo ds. i have done research & from what i found everyone says that it works or its supposed to because the ds is region free apparently but every time i put it in and start my DS it doesn't read the game it acts as if there's nothing in it, somebody pleasssssse help me!!!!! I cant tell if i should be mad at the seller since its brand new, or if something is wrong with my DS, but please! Someone help!!!!!!!