If you receive a call from an unknown virtual number, you can trace its owner by using tools available online. Try reverse phone number lookup sites, which can either be free or paid. You can also set up your device to display CNAM (caller ID name) and IP address, since caller ID alone is easy to fake. If you have your own virtual number, you can do a CNAM lookup with your VoIP provider.
If you suspect that a caller is faking their outgoing caller ID, you can use a CNAM lookup tool to get the CNAM data you need. As a last resort, you can try an IP address lookup, which should tell you its location, internet provider, and domain name.