Not double booking, but one of my Ts was quite disorganized and made a mess around scheduling and other administration many times. His thing was calling me at the time of appointments that I canceled well in advance, to ask where I was. It happened 3 times within 1.5 year. He never apologized (for anything, in general), just told me that he did not remember my cancellation and I should remind him the day before. WTF?! I was really pi$$ed off the last time it happened and we had a huge fight on the phone over it.

Maybe double booking accidents can happen, but that note by your T about not sending an angry text is condescending. The fact that you were respectful toward the other client has nothing to do with how you felt about it, and you absolutely have the right to tell a T that.