Welcome to a server full of very toxic people, including admin. You are right, this shouldn't happen, but as you can see- players are a cesspool of toxicity because "get gud" is all they have going in their life. So why change it?
And prepare for Admin to say "There are no rules against having a character in both factions and there are no rules againt multiple accounts" It's a co-out to avoid mediating. Because, you see, mediating is "work", why bother with that? =]
Best you can do is try to chill and don't engage with these ppl further. It's healthier.