That’s that
Definition 1 of 2
Pro Tip 1/3Resolute Closure
Used when a person is set in their decision, expressing firm finality with no room for debate. 
He announced his retirement, and that's that.
Pro Tip 2/3Conversation Ender
Marks the end of a discussion, typically because a decision has been reached. 
We're not buying the car, and that's that.
Pro Tip 3/3No Alternatives
Implies no other options are available or will be considered. 
This is our final offer, and that's that.