credit ban but i don´t know for what?

hello, i´ve played yesterday with 3 friends (they played halo the first time in their life and are women^^) Halo Reach multiplayer. We´ve played 5 or 6 rounds in Premium battle. Today i start playing Halo Reach, after the sign in a message pop ups and says that my Xbox and my Gamertag are banned for earning credits. I think i was banned because the game thinks my guest are AFKers because they have the most time 0 kills. But the tried to run and kill others, in invasion they put the bomb in the zone and more, but the game can´t differentiate between AFKers or bad player.My question is, is this normal, and how long will i be banned?My Gamertag is: ScHwOnSeN

that would explain it. next time try and get a bit more practice with them first in campaign or something so they dont get mistaken for AFKers