I don't think you're being unreasonable. I think it was a good move to write an angry note and another good move not to send it.

I'd suggest sending a note (or asking directly, if you can) in a very neutral way, asking about the request to move your appointment again after the feedback you gave last time that you were very upset at being asked to move it. I'd keep emotion/accusation out of it as much as possible - for example, asking "what were the reasons for..." is more neutral than "why..." or "how could you...", "didn't you think that..." etc. Then I'd give your T space to respond.

Your emotions around this seem absolutely valid. Unfortunately, I think they also give your T a possible distraction and a way to focus this issue back on you. If your question's factual and neutral, then that means your T needs to consider his decisions/actions and his reasons for them. It's also more likely that you'll find out what was really behind it. Maybe it was an oversight, poor communication with his assistant, a misunderstanding etc or maybe your T really didn't listen or didn't respect what you said.

When you've got a response, then I think you could talk about how that makes you feel. If you can hold back the anger until that point it gives you more power in the situation. Establishing all the facts before reacting is a very powerful thing to do, and it would create a pause in which your T needs to do some thinking and give you a proper response.