That’s that!

(and) that's that

That is final; the issue is settled or completed. You are going to your sister's recital and that's that! No more complaining. That's that! I just send the proofs to the printer. Let's just say that's that and be done with it.
See also: that

That’s that!

exclam. That is final!; That is the end of it! I said no, and that’s that!