As already indicated..report them.
However.... you will likely be asked to blacklist and such.

If it becomes a worrisome thing you should consider transferring servers.
In truth....the other issue (lodestone) is a waste of time.

Consider it a compliment your being mimic'd. Get on/move on. Like it or not anyone and everyone is free to glamour as they see fit.
If you wan't to be a real annoyance..start dropping fantasia potions...kind of forces the issue lol. (Yes your spending money but it would be funny as its forcing them to do the same as well)

If it corsses over into other social media sites....you have the option to contact Local Law Enforcement.
Cyber Bullying in many states....is not a good idea.

In truth....black list...file a harassment petition if necessary...and just ignore them.