Surely there's no need to drive down there if their phone number is listed in the whois information.
The mail server ip address listed in whois does actually match the one in the email headers, so the spam is definitely coming from them.
The only question is, are they doing it on purpose or has their email account been hijacked?
Perhaps a phonecall would sort it out. I'm not on the same continent, but does anyone live in the states, and fancy giving it a go?