Voicemail not working

Contact your cellular carrier. That's a carrier feature.

my Voicemail is not working can’t leave message

If the person you are calling does not have the voicemail turned on, you will not be able to leave a message.

Call your carrier voicemail box and listen to the main menu.

An example from my carrier:

Call 12331 to turn On voicemail.

Call 12330 to turn Off voicemail.