Best answer by Adzdalton
I've seen this problem a little while ago.
I'm not sure what version of android this solution worked work on.
If it was an older version this may not work.
I don't have an S7 to test it on but you can have a go for nothing.
Settings > Connections > Apps
Then there were 3 dots at the top right of the screen. Click that.
Select Switch on System apps
Scroll down to the first of 3 Phones and select
Select "More settings" at bottom of drop down box
Select and enable "Wi-F-calling"
Go back to your home page and turn off you phone and reboot.
Hope that works for you