I've encountered the same thing - twice. Most therapists seem to be reluctant to see a client before the client had ended properly with their current therapist. In a way I can understand this - termination is an essential aspect of the therapy and any good t probably knows that it needs to be dealt with properly so that the client is reasonably able to find closure. If this isn't found, it can seriously mess up the next therapy- or indeed any - relationship.

That said, i do think there should be freedom of choice to explore when a current therapist isn't working out. We don't always know if/when we want to leave one T before looking around to see who else is out there. Perhaps being honest with any potential ts at the session is key.

I hope T1 responds to your email and that the final session is what you want/need. Do you have the option to return if you change your mind? I hope so as that might help.