Ipse, I don't know that formal action will accomplish anything for you, make you feel any better? It certainly can't make your therapist "come back." I had a literal medical malpractice problem a few years ago and ended up not seeing the point in doing anything about it; it's a lot of work that wouldn't really have helped anything.

When my husband left his first wife, moved out to an apartment of his own, he gave her a very generous amount of money twice a month with no settlement, no legal requirement. His first wife was a bit naive and called social services and ask them to literally "get him back." They first worried/asked her about legal agreements and "isn't he giving you any money?" and she explained the situation and how much he was giving her (without any sort of agreement, no legal "need" to but just because he is a "nice" guy) and they actually laughed at her. You can't force someone to love you/live with you.

Too, since you are the one who "took a break" three months ago and you all weren't seeing one another again yet, I don't know that anyone legal would see any grounds for your action. Your therapist merely took her option of not wanting to getting back into therapy again with you. She's "allowed" to do that, no matter how poorly she does it. She did it legally with the letter, she's talked to you on the phone; I don't think there's any other legal obligations she has to do. Legal actions would only look at legal obligations, not moral or hurtful, etc. ones.