This is what happens in every shard and will never stop, and also seems like the game EM/DEVS/GM give bragging rights in some sense to the PK/Red players, as its arguable they are playing a roleplay of a killer and they are just taunting you for not being able to kill them..... and its just you getting your pants in a twist by desperation, Not saying this is the case here but its a very difficult and arguable matter....
To my knowledge there is a few steps as Morgy says:
1. Ask them to leave you alone and stop harassing you in a polite manner (Preferably like 10 times or more) Screen shots help here....
2. Still keep asking them to leave you if they follow you, the more you ask them to stay away the better, have friends also be able to verify this.... (Pictures)
3. Block them from the chat options by selecting to ignore them, But If you are being attacked you wont see the name of the spells the cast either....
4. One were most people fall into the trap too, Block them from ICQ, Vent, TS and all other chatting services, That can also be used as harrasment....
5. Take your space from them, If they are bank sitting in Luna, dont just go and stand next to them, take actions to avoid any sense of contact, be in a different shard if posssible, The more space between you, the easier to ignore and not get into trouble. Also shows initiative to avoid the confrontation, so works in your favour.
6. Have plenty of time in your hands, as this wont be done over night, a couple of emails and a couple of tries will be needed before anything gets enforced from the TOS rules. In many cases, the wanted justice wont come as your claim wont be backed up properly by the rules and will get overthrown for lack on TOS rules, so dont get angry, just try again, If in worse scenario, Email the big boys ingame.... Messna and the GMs