Do Not Disturb iPhone 12

Here’s a list I’ve compiled of possibilities.

FIRST—Are the missed calls in Phone/Recents on the phone? If they are not the problem is in the network, because the calls aren’t getting to your phone. Contact your carrier: 

• check with your carrier that they don’t have a local outage, and that you didn’t have any settings that would have immediately invoked voicemail
• check up on them at Down Detector - outages

If they are in Recents here’s what to check next:

• Check the MUTE switch on the left side of the phone, above the volume buttons. It should be towards the screen and should not show red when you look at it from the side.
• Check the volume setting. With the Home screen displayed, press the VOLUME UP button on the left side of the phone. It’s above the VOLUME DOWN button and watch the volume gauge.
• Go to Settings/Do not Disturb. Turn it off if it is on. Also turn off Scheduled. With both off none of the other switches there matter.
• Go to Settings/Phone. There’s a switch for Silence Unknown Callers. If it is on any calls from numbers not in your contacts will go directly to voicemail.
• Also in Settings/Phone: Make sure Call Forwarding is off.
• Go to Settings/Sounds & Haptics. Make sure there is a loud sound assigned to Ringtone. Old Telephone is the loudest.
• Go to Settings/Screen Time/Communications Limits. Tap each of the 2 entries and make sure both are “Everyone"
• Restart your phone-->RESTART your iPhone, iPad, or iPod touch - Apple Support
• If all else fails, talk your carrier into replacing your SIM card (thanks to ASC user DShelbyD)

The settings “Always” and “When iPhone is Locked” only have meaning when Do not Disturb is enabled. They are ignored when DND is off.