Not to defend how this was/is dealt with, but there is at least 1 thing you can do. Read the ToS right now. It could give you a clue about what you may have done. So if you read a part and go "oh I didn't know I wasn't allowed to shout that someone early pulled a hunt mob" (for example) then you think back to doing that and if that's the only thing you see that you violated then that was probably it.

Again, not defending this idea they shouldn't tell you what it was about.

But also, even if you read the ToS and don't see something that makes you realize what it was, you'll at least have a fresh look at what's allowed and not allowed.

And some of it is crazy sure, like a guy can join an FC and empty their company chest, and that's OK, because SE will say it's up to the FC to manage permissions, but the moment you shout that this player did that to you and include their name, you're in the wrong. Even if you don't agree with it, knowing how SE sees things can help.