Just so you know, which I am sure you already do, this is actually a case of "indirect" bullying which I was subject to by a previous boss and director.
It's about being ignored and isolated (indirect) as opposed to being tripped up in the playground (direct) etc.
This is almost the worst case of bullying to prove as some people (especially in my case) either never witness it or think we are imagining things. It's only when the bully slips up do others start to realise what we mean.
You are professional and so far seem to have dealt with this very well but it's not fair that you have been subjected to such childish bullying behaviour.
Personally I would love to shove their two heads down the toilet but of course we never lower ourselves to that of a bully.

Good luck and keep us posted.