ISPs have your contact information, and they can also put up notices on their own website. Hijacking somebody else's website with forged replies isn't "the way they notify you," it's a man-in-the-middle attack, and users shouldn't be trained or encouraged to accept it.

> ISPs have your contact information, and they can also put up notices on their own website.

So whenever you see "Connection Refused" your instinct is to go to your ISPs website?

I also don't think it's "hijacking someone's website", then it'd be global, instead it is a man-in-the-middle attack, serving different traffic than the user intended.