Do you mean:

  • I got a Missed Call notification but my phone didn't ring!


This is not so common but possible when you use Silence Unknown Caller or Call Blocking & Identification i.e. filter options.

To learn about the same, please follow the Apple website.


Also, 

Please ensure Do Not Disturb feature is turned off:

  1. Go to device Settings app 
  2. Tap Do Not Disturb 
  3. Ensure it is disabled (or turn it Off)


Please ensure the device time & date is set to Automatic:

  1. Go to device Settings app 
  2. Tap General
  3. Tap Date & Time
  4. Ensure Set Automatically is enabled (or turn it On)