This # is filling up my mail box with silence

this number calls me once a month excatly every 3rd saturday of the month and always around 6pmI dont bother to pick up

This number has called me 3 times in the last 24 hours.  A computer voice says "on behalf of Key West Ford 520-3055" and then hangs up on me.  That's literally all it does, nothing else.

I tried to 411.ca it and find out who it is... but got nothing. Apparently, the number doesn't exist... it could at least say 'private' or 'undisclosed' or something to say they don't want to give their name...
Either way, there is no reason for a car call center to phone me because my car lot emails me directly... and has previously phoned me directly, and their name as saved in my cell phone appears on the display so I know it is them.
They also like calling me while I'm at work... which even if I did hear the call, odds are I won't answer them unless they get lucky and catch me on break.

Who keep calling me without any answer?

They called me on behalf of signature Mazda regarding my servicing.  Appears to be a call centre.