I don't think you are being the least bit oversensitive. I would be very angry. I really like Echoes' idea about asking for a free make-up session. If he agreed that was fair, then it would be some attempt on his part to be a "stand-up guy" about his responsibilities.

Sounds like he's spread himself too thin. He is not providing all that he is being paid for, and wanting to make as much money as he can might be the his motivation. And to top it off, you say "it has happened several times before". He's got some nerve!

You had every right to email him. I hope you expressed that you feel he has been under-serving you. There is no way, no excuse, that what he is pulling is okay. AND he should affirm your dissatisfaction as being legitimate and apologize to you. If he tries to turn it around that you are unreasonable, then he is a total creep. He is being very non-therapeutic in setting you up to be accepting of what is not acceptable. One of the goals of therapy is to learn to have appropriate expectations of others. Don't be suckered by this guy. He is taking advantage of your self-doubt. He is very unprofessional.