First, he tells me that we are no longer going to communicate in writing/email...
I don't understand how he can unilaterally impose a written communications embargo.
I hesitate to make any snap recommendation without knowledge of the specific policies in your district. However, I should think that the matter could be addressed by continuing to communicate in writing by email or registered mail, keeping a record of ignored communications, and launching a complaint with the superintendent. A complaint citing the comment by the principal would also help in indicating that the lack of communication is deliberate.
Many busy parents are unable to schedule calls or face-to-face meetings during a (unionized) principal's work hours. I can't think of any industry where refusal to communicate in the client's preferred mode of communication would be acceptable.
