Go to the mediation session anyway and see if there is any kind of documentation they will give you stating this was scheduled more than once and mother refused to show, then File Contempt!
Use everything you have including the messages from her stating the accusation of abuse was made to hinder your access to your boy.
I would not make any attempt to contact her at all directly as she may try to use it against you because of the protection order. (doesn't matter if the order only says phone contact, she could try to have you arrested if there is any contact) I would ask the mediatators if there is anything they can do for you to facilitate visits during the holidays. Also ask them for suggestions on scheduling visits.
Your currect CO is for supervised visits, but I am assuming there is some type of schedule on when, where, how and who. You will need both a noterized statement from whomever is supposed to supervise visits and a promise from them to appear at a hearing if at all possible.
ANd one more thing NEVER, EVER take her word for anything. ALWAYS appear for any scheduled hearings unless you have something in writing from the court stating the hearing was postponed or cancelled!