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
Farlex Dictionary of Idioms.

That's that!

Inf. That is the end of that! Nothing more can be done. Tom: Well, that's that! I can do no more. Sally: That's the way it goes. Doctor (finishing an operation): That's that! Would you close for me, Sue? Sue: Nice job, Doctor. Yes, I'll close.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.
See also:
  • (and) that's that
  • And that's that
  • That’s that!
  • that's that
  • that's more like it
  • that's just it
  • that's all
  • that's right
  • that's a shame
  • That’s the stuff!