I received a fax on my E-Fax number from 708-538-0173 trying to sell insurance. It was a one page ad listing rates and telling the recipient to fill in personal information and fax it back to an 800 number.  Of course, there was no information on who they were- not even a fake company name.  It may not even be insurance they really want to move - it may just be a ploy to get personal information. Efax.com is a fax through e-mail service which uses real phone number, which they lease to you on a monthly basis, so you do not need a fax machine.  

Likely it's a spoofed number.