As bridonca mentioned, Freephoneline has nothing to do with you receiving spam calls.
If you use this guide fully, you'll learn how to use your OBi202 to block or route known telemarketer calls elsewhere:
http://forum.fongo.com/download/file.php?id=2065.
However, it's unlikely 5878874869 is the real phone number. People are able to fake or spoof whatever outgoing phone number they want.
If it is the real number, since it's a Fibernetics number, you can report it here:
https://www.fibernetics.ca/legal/nuisance-calls/