Why wont call of duty mw2 work on my xbox 360?

My old call of duty mw2 was scratched upi and i bought a new one at gamestop. that new one on my xbox told me to wipe it even though it was new. so i returned and got a new one. but that one is still saying that it is unreadable. i would play like one multiplayer match and then the thing would just pop up saying that the disc is unreadable. please help me figuring out why this is happening.