Do not disturb

That is because you have it set to allow calls from Everyone. You need to restrict who you allow calls from, or it won't do any good. Set it to Contacts or Favorites, otherwise with it set to Everyone, then all calls will be allowed in, which defeats the purpose of Do Not Disturb.

I am guessing, but you are using another phone to call with? If that is the case, then you should not get a busy signal, but the call should go to voicemail, and you would not receive a notification. No call and no notification is the correct behavior for Do Not Disturb. That is what it is for, not to disturb you.

What happens when you try? Please better describe your issue.

Thanks and regards

Giulio