Multiple calls to all of our phones (16) day and night sounds like a fax tone but it is not a fax

Got a call on Saturday at 9:19pm EST sounds like a fax machine but my fax did not pick up.  We tried to call back many times but the line is continuously busy

THIS IS VERY ANNOYING. . .I SUGGEST THE PHONE COMPANY TERMINATE THE SERVICE FROM THIS PHONE NUMBER.

Automated call, message states "That is not a valid entry"
Likely dialer looking for valid phone numbers to put on call lists

I have gotten several calls from this number; but no one is there and no fax comes thru.  It is annoying....