It is a very difficult work to check who called you when you don't have his number saved. It is not difficult if you have truecaller. Truecaller allows you to check who called you even if you don't have his number saved. 


So, Open truecaller app and then register. Registration sometimes gets itself. It sees the number of the sim in your mobile and then login it without any otp or validation. 

The first thing you can do to check who called you is to click on blue button on the bottom right corner. After clicking it, a dial bar will appear. Type the number and it will show you the name. The other thing you can do is to copy the number you want to search and automatically it will show you the name of the number you copied without even opening truecaller. Download Truecaller here-Open In Play Store