As you know, many of the other Board members had the Troll on ignore for quite some time before he vanished. It's possible that he can only send PM's to those who have not placed him on "Ignore". Only Moses would know the answer to that.
If by chance the Troll can still find a way to send his victim a PM after he's been placed on "Ignore", than that falls under the definition of "Cyberstalking", which is a criminal offense in certain jurisdictions.
You may want to check with Moses to find the best way to handle this.
You may also consider saving an electronic version of any/all messages sent to you by the Troll as evidence if ever needed for legal purposes.
There's more than one way to skin a cat.