all calls go to voicemail

Please follow this path,

iPhone > Settings > scroll down > Apps > Phone (use search field at top of page or tap P along right edge) > scroll down > Silence Unknown Callers > disable, if already off, momentarily turn on then back off

Do you have silence unknown callers turned on?

Settings > Scan all the way down to the bottom and tap Apps > Tap Phone > Make sure Silence Unknown Callers is not on.

If that's not it, the next step would be to contact your carrier and ask them to help you.

Might you have set Do Not Disturb?

How to turn Do Not Disturb on or off on your iPhone - Apple Support