So I'm understanding this as:
"LINE Webtoons has a rule that once an artist becomes Featured, their content is supposed to only be updating on Webtoons. I've seen artists breaking the rule, and when I messages Webtoon about it, I got an auto-reply in response. When I messaged them again, I found out my emails weren't going through anymore, as if they'd blocked my email address."
I'm going to be honest, I'd find it frustrating to see others breaking the rules, but it doesn't seem worth taking personal offense to the point of making you sick! I don't think there's anything wrong with alerting Webtoon to the fact that people seem to be breaking the rules, but if they don't want to deal with it then...... that's up to them? Maybe they don't care, maybe it's an unwinnable fight and they're picking their battles..... who knows.
Unless you are also a featured artist, I honestly don't know why it would be anything more than kinda frustrating. It's Webtoons' battle, not ours.
The email blocking, though, seems like such a weird move... I'm not very tech-savvy, but I have to wonder if it wasn't an intentional block. Like if an email client automatically and incorrectly labelled your account as spam or compromised with malware or something. It doesn't make a lot of sense to block someone who sent only one email?