Considering you basically just were unbanned, a ban for the same reason, mind you, no warnings were issued, as you know the reason.
Opening the gate, when there are quite literally enemies standing in front of it, is one of the most stupid things to do. Your friend, or teammate, did not close the gate, as opposed to what you told him. If someone is directly behind you and you do that at the beginning of the round (read: latest 30secs after first initial spawnwave), we might not react to it. You though, did it 2minutes before the end. No earlier unban. This is not negotiable. I'll reserve judgement to even make the ban last longer.