I suspect these ‘people’ have more than one line on the go at any one time.
There’s a big spate of spam calls to my employers work mobiles at present. They start by telling you they are calling from O2 (who do not supply the mobile service)
I usually manage to get them to hang up very quickly by replying with a stream profanity, and advice about their career choice.
Childish, but it makes me feel better.
54-46 was my number