Q: DND

Hello there Modyalex,

It sounds like Do Not Disturb is not working correctly, and is allowing all calls through from everyone rather than just your Favorites as you have set it. I would suggest turning it off first:

Tap Settings > Do Not Disturb.

From: Use Do Not Disturb on your iPhone, iPad, or iPod touch

Then quit the Settings app:

Force an app to close in iOS

1. Press the Home button two times quickly. You'll see small previews of your recently used apps.
2. Swipe left to find the app you want to close.
3. Swipe up on the app's preview to close it.

 
When you have done that restart the device and test the issue again:

iOS: Turning off and on (restarting) and resetting
 
If the issue persists, backup your device to iTunes, then restore it as new and verify that it works. 
 
How to erase your iOS device and then set it up as a new device or restore it from backups
 

If it does, then restore your backup to either verify it still works and the software just needed reinstalled, or isolate the issue to the backup file itself. Thank you for using Apple Support Communities.