Dear T,
How nice of you to bill me for last week's sessions without replying to my email. I know that was for services already rendered, and I'm sure it's much easier to invoice than to reply to my email. But I'm starting to doubt you'll actually reply "this evening" like you said earlier.
I'm not going to say anything unless you haven't replied as of late morning tomorrow. Though that would be along the lines of "don't bother; we'll just talk Monday." I just worry that the last time this happened, it was because you were confused by my email (as you said later) and just kept putting off replying. I gave you an easy out today--saying that if you were too busy or if you preferred to just talk about it in session, then no need to reply beyond acknowledgement--why didn't you just take it?
Maybe you'll reply later tonight or in the morning. It had better be at least somewhat supportive and not some defensive screed. If it's going to be the latter, just say "let's talk in session."
Love,
LT