My 61 year old dad is semi retired and works from home. He has a standard phone line and a fax line. He got a call on the fax line while I was in the room. The guy identified himself as being with Publishers Clearinghouse and my dad told him politely that the number he’d called was a dedicated work fax line. The guy, loud enough for me to hear, responded FUCK YOU!
My dad hung up, then tried to call the number back to speat to a supervisor. No one answered.
Highly unlikely it was actually Publishers Clearing House.
Yeah, this screams “scam” to me.
I’m confused… I would assume a dedicated fax line would have a fax machine connected to it. Why did your dad answer instead of letting the fax machine pick it up? 
The obvious response to people selling something is to simply hang up.
If the dedicated fax line is getting call after call from the same number and not interfacing with the fax machine, I’d pick up out of simple curiosity. If someone’s innocently dialing a wrong number, it does no harm to let them know that Kenny isn’t here, and this is a fax machine phone number so no one will take a message for Kenny.