Caller ID is fundamentally broken and scammers are SPOOFING (telling a lie) the number so you can no longer count on the Caller ID number to be correct.
If you don't know this number, don't answer as it only fuels their system as "this number answers, I'll tell my spammer friends about it."
I recently missed a called from 01733 023365. I've tracked the area code to Peterborough, Cambridgeshire. Normally I would ignore a missed call, however I have recently applied for a few jobs and I work in a field in which many companies are based in Cambridgeshire, and so I'm concerned over whether it was a call related to one such application or not.