my only advice in this situation is to get with an Advocate and get their advice. They will have more practical advice and I also think you may consider speaking with an attorney who is familiar with special education law. They may have some ideas for you.
IMHO, it seems odd and abusive for a principal from another school to have any contact with your son at all. It seems like they are hiding something because they never brought you or your spouse into it. I am concerned that your son was not allowed to call you either. I would certainly discuss this situation with his case manager and find out what happened.