why is the message I receive when calling "number not assigned"

Apparently, you are calling a number that’s not active.

Make sure you have the right number. If you have confirmed with the person/entity you are trying to call that you have the correct number, contact your cellular carrier for help.

Each carrier in each country has different way of supporting shortcut numbers dialing.

Contact your cellular carrier and check with them if the one you're using is okay for them.

Regards

Giulio