Hard drive ignores available free space
The following solution assumes some comfort with the command line - if you aren't comfortable with it, let me know and i will provide a GUI method.

Referring to your picture, 


click on the line that says "Container disk 1"
make a note of the value in the field "physical stores" (let's
assume it says disk0s2)
In spotlight type 'terminal' and hit return to bring up the command
line
become an administrator (either su to the administrator or login as
one)
type the command 'diskutil apfs resizecontainer disk0s2 0' (change
disk0s2 to your value).


When the prompt returns, you should have the whole disk back. If not, please make a note of the result and publish it here.