Hi,
If someone attacks you repeatedly, and sends pillages, as annoying as this may be, it is not considered an abuse. That is why it is a limit to how many pillages a player can send a day and also how often a province can be pillaged. However, verbal abuse can and will be punished by the game administration.
As per the fortress sieges just try to spend resources and leave him no reason to attack, until you get strong enough to surprise him.
And just remember, sometimes the best defense is the attack
I hope this helps.
Cheers
