I recommend you should start by adding him to your block list, you can do so here:
https://forums.d2jsp.org/pm.php?c=14If he keeps harassing you in your topics or via goldlog for example, you should report him to the appropriate staff member.
E.g if it's in your trade topics, report him to a
Trade Moderator , and if it is in any discussion forum, report him to a
Junior Moderator