Firstly - stop panicking
Secondly the community here is the first line for any questioning
What phone do you have?
I have 2 Android phones and sometimes when the device has rang the number hasn't appeared. The ringtone has sounded but all that was displayed was the home screen.
Both of my devices run Android 9 (stock ROMs)
Were they phone calls? You should find the number in the received or missed calls list
Or if the person rang on a service like WhatsApp that's where you might find the details
Or you could have been really unlucky and the number didn't register on the list if your device shut down unexpectedly.
Did the caller leave a voicemail? or they may have emailed you instead?