If you are getting kicked, you are playing Player Matches. The kills you obtained have not been counting towards your achievement. You need to play Ranked Matches. If you can't join any, it's probably because they have filled up before you were able to join. Not many games are hosted, so people always rush towards matches that are almost filled. Best solution - Host. It gives you an advantage in-game plus it ensures that the game won't end due to a quitter.
Also, the DLC maps are Bullet Marsh, Raven Down, Subway, Garden, Process, and Old Bones, so if you can't download the DLC for whatever reason, stay away from them.