Rate me puzzles, but....
Get his name, try and get an extension or employee number to go with it (he'll probably lie, but whatever), tell him the date and time, make a note of it, screencap your phone being on the call while you're at it, and tell the guy that you're telling him and his compa y to stop contacting you and that any further communication from them will be considered harassment and you'll file a complaint with the police.
Actually file a complaint with the police if they continue, cite the date, time, and any other documentation. If it's by mail file a complaint with the post office.
I was able to get a couple of really persistent companies to stop bothering me by threatening them with a police report,