Fix this plz

This game is a great game. I love zombies a lot but there has been a few glitches that I have seen. There is the one where zombies can go through walls and were a zombies is unkillable plz fix this I dont want to play a game and have to end it there because of this also its very easy my first time playing not knowing what to do I made it to round 34 just asking make the game hard but not to hard

Aim to kill about Call of Duty: Black Ops Zombies