ABCDEF7 · M
1. Restart phone
2. Settings > Sounds and Vibration > Do Not Disturb > Check all settings including Advanced.
3. Settings > General Management(or System) > Reset app options
4. Settings > General Management(or System) > Reset > Allow exceptions
5. Check for the updates if available, if yes install them.
6. Try force closing all apps one by one and check if DND starts working. Maybe some app is not letting your phone go DND. Find the culprit and uninstall it.
7. Try installing 3rd party DND Apps.
8. Backup all your data. Settings > General Management(or System) > Factory Reset
9. Go to workshop
10. Buy a new phone
2. Settings > Sounds and Vibration > Do Not Disturb > Check all settings including Advanced.
3. Settings > General Management(or System) > Reset app options
4. Settings > General Management(or System) > Reset > Allow exceptions
5. Check for the updates if available, if yes install them.
6. Try force closing all apps one by one and check if DND starts working. Maybe some app is not letting your phone go DND. Find the culprit and uninstall it.
7. Try installing 3rd party DND Apps.
8. Backup all your data. Settings > General Management(or System) > Factory Reset
9. Go to workshop
10. Buy a new phone

SW-User
Put your phone on flight mode and switch off wifi calling.