If you are using smart phone than truecaller will help you identify any unknown number. Its vary useful and easy to use app. Just install and sing in to the app than it will help you with its various features.
Its has a feature which help you when you get a call from unknown number than it will search its directory and show you the caller name and location on your calling screen.
It has its own dial feature if you enter any number on that dial screen it will show you the name of that person and also you can call from that dial screen. Don’t need to open phone default dial app.
Truecaller has many useful feature, you should try truecalle.