DH and I sleep days, and it was so incredibly annoying to be woken up every couple of hours.
We've tried various apps, without little or no success. Finally I got so fed up that I put my phone in constant "Do Not Disturb" mode, and set it to where only people on my contact list can get through. Everybody else gets sent straight to voice mail without the phone making a peep. Ahhh. Silence!
When I wake up, I check for any calls, and look the numbers up on Google. Most of the time they're scammers, robocallers, or telemarketers. Ugh! They get blacklisted. If they call again from that same number, they get a message saying that my phone has been disconnected or is no longer in service. If they call from a different number the next time (and they often do), I'll blacklist it as well. It takes time, but I rarely get these unwanted calls now.
DH hasn't been doing this as consistently as I have, and he still gets a lot of unwanted calls.
The less-than-ideal part is that if you're expecting a call from (say) a doctor's office, you have to have their number(s) in your contacts list or they'll get sent to voice mail without your phone ringing. Or you can turn off "Do Not Disturb" until that call comes through. (You just have to remember to do it!)
My phone is an Android phone, and the "Do Not Disturb" settings can be found under the Settings icon (it looks like a little gear). To blacklist an unwanted call, go into the call log, long-press on that phone number, and a menu will pop up. "Blacklist" is one of the options. (I'm not sure about other types of phones.)