First of my I kinda fucked up with not responding earyler, comp upgrading and other things got in the way so really my bad.
Now a few things about your post.
When I went into the room, I placed it down to close the door behind me,
False. You brought the barrel into the room and
stayed in the room, had you closed the door you would have survived the explosion.
and Symbolzzzz decided to just shoot the barrel, killing us all except for one person.
False again, I was not the one to shoot the barrel. I can't recall the name of the person that did it but he got his karma knocked down to around 500 and the events log had his name on all the kills. I am pretty sure he got banned as well, but I am not certain.
In addition, if I were to be killed for HAVING the barrel, you WOULDNT shoot the barrel, you would just shoot ME and then move the barrel away.
I
was shooting at your face with a deagle, but since its TTT the headshots registered as bodyshots and someone shot the barrel before I managed to kill you.
Now onto this the ban itself.
The rule for shooting explosive barrels (and I discussed it with towere
before banning you) was that the kills made by someone shooting the barrel went to the carrier of the barrel, rather then the shooter.
This in mind you got 6 teamkills with that barrel, that is mass RDM that in turn is a permanent ban.
You broke the rules and got your punishment.