Maybe the app you installed recently is the reason for this problem. Try uninstalling the app and check if your device starts ringing.
Maybe a temporary software-related issue prevents your device from ringing. Try restarting your device and your device should start ringing.
See the don't know how to restart my device guide if you are not sure how to restart your device.
If you tried everything else, but you were unable to fix the app which doesn't ring when a notification arrives consider uninstalling the app, via Google Play (Android devices), App store (iPhone) or Windows store (Windows phone OS).
If you don’t receive the email in the next 2 minutes please check your junk folder, and add [email protected] to your safe sender list.