Who called me
When you work with computers and possess at least one certification in cyber security, you tend to have friends or family that call or message you on occasion asking you to trace a phone number for them as if you are some form of digital private eye.
The truth is that only the authorities with the assistance of the telecom providers can legally do that. All these websites that say they can trace any number in the world for you are lying. They are just scams after your money. At best they have scraped open source content for numbers and can tell you the network provider, country of origin, and anything that is available online for free. Maybe they’ve concatenated and absorbed phone directories and public domain phone number repositories. They certainly can’t trace an unlisted number for you.
That said, if the number does have a footprint of some kind in the public domain then there are ways of finding it. Using Google Dorking to scour search engine data may uncover something useful. Governmental company registration databases that are open to the public may also reveal data. Whois records, club memberships, company websites, etc.
The phone number is just a character string. Play with the format when searching. For example if you were called by 07709 123456 and you are in the UK you could search for exact string matches of:
07709 123456
07709123456
7709 123456
7709123456
44 07709 123456
44 7709 123456
4407709123456
447709123456
Google for OSINT tools and techniques related to phone numbers for more suggestions.