If it meets the conditions of Ongoing Harassment they take that seriously. You have to report it correctly though. Ignore puts the account on Ignore, including every char on it - you have to do it on each of your chars though.
If someone were doing that then that is terrible. It is one of the reasons that Char-server the way we have it now is less secure. People can add your char, mail you, track you, see name changes, etc without your permission. On the forums you have to ignore them on each character.
Battletag on the forum means they can’t do that. They can’t talk to you at all outside the forums without your express permission. A friend request can be dealt with as a single click decline and block all at once. They can’t see your chars if you don’t post with them. They can’t contact you. You can Ignore the whole account on the forums, not char by char.
Also, keep in mind that just replying to you is not considered harassment on the forums. Even if you have them on Ignore. They don’t get penalized unless they are actually breaking the rules.
Edit - here is the info thread on Harassment and Ongoing Harassment. If it ever happens again someone will be happy to walk you through what you can do and how to get assistance.