While I personally disgree with a length of 30 days, in this situation I can completely understand to go straight to bans after a warning with admin chat.
Seriously, at least on EU I am pretty confident that players listen up as soon as the red text appears cuz it's rarely used for nonesense.
If an admin uses the red text: pay attention and listen!
9 people all shouting at an admin, most likely spamming the 'i' chat, nobody listening to your warnings, instead even more spam and caps lock in the chat?
I'd have dealt out bans too, just to get the situation most comfortably and secured under control.
Probably just 1h or 2h bans but bans nonetheless...