Spoofing email and phone caller ID is actually really common these days, but line-tapping is also active in some places.

Call the persons extension back from an out-of-band line, but after checking the contact phone number on the old web page or government business registry.

This is effective against most forms of line tampering, as targeting an unknown random line number is much more difficult to predict.

Most nuisance calls we get are the classic foreign operator message repurposed language translations trying to get people to "press 1 if you like ice cream" which bills 3rd party long distance calls. There was a local dubious calling card scammer arrested twice for this con. Just hang up, and report/block the number =3