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. © 2015 Farlex, Inc, all rights reserved.

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. © 2002 by The McGraw-Hill Companies, Inc.

That’s that!

exclam. That is final!; That is the end of it! I said no, and that’s that!
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions Copyright © 2006 by The McGraw-Hill Companies, Inc. All rights reserved.
See also: