Received call attempt from this number about 1.5 hours ago. I say 'attempted' because the call-block app I use auto-blocks all calls and text messages from numbers not in my Contacts list, without ringing my phone at all. It stops the nonsense! Needless to say, I did NOT call back.
If it's an important call, then a voice-mail is usually left and I receive a notification. If it turns out the voice-mail is still garbage, I change call block options so that future calls from that number are rejected in a way that bypasses even the voice-mail system. Unfortunately, for most cell users, the app requires that you have 'Super-User' permissions on your phone, meaning that you need to 'root' (Android) or 'jailbreak' (iPhone) the phone aka 'hack' it. It is not something recommended to the non-technical person... As even a single mistake will typically result in your phone becoming an expensive 'paper-weight' and you needing of a new phone.