Sorry about this, it seems more complicated than I anticipated. But since it's just A hater (singular), you can probably deal with them easier than if it was a group. Just try to not let them get to you and whatever issues you may have, I hope you'll get through it successfully.
Ceejaythe630th
That's life, people will hate each other even if there is no reason to. Technically blocking them would be the more simpler thing to do, but reporting them to the postal police sounds like another good idea.
ItaliaNinjArtist
Eh, but... there is a problem but if I write it here, "that" will bother me endlessly.