This is an automated call stating they are from "Revenue Canada". The message is something along the lines of "you haven't paid your Taxes yet....."  The robotic voice was VERY, very slow and said "Please call us back at this number....." and I hung up.  this is obviously a Scam because the REAL Revenue Canada would send you a letter clearly stating whom they are, etc.  So I'm putting these people on Call Block.
My concern is they can call someone who could be Elderly or had something happen and not be thinking as clearly as they normally would and call that number back and fall prey to these pathetic people.

same as O.P.
do not call this number back. It is a fake call.

Same as OP.

Received a call tonight from this number on my vm something related to revenue Canada hard to understand message so I called number but no identification when vm kicked in.  Guy calls me back and I told him right away this was a scam, we mailed u something and u didn't respond that's why we're calling.  Put it back in the mail I told him.  Disgusting people do this and prey on our most vulnerable.

Voicemail message indicating that I was being audited by Revenue Canada and that I had ignored previous mail inquiries etc.  I very firmly explained that I received no such communication, and was angrily questioned the validity of this 'audit' the ''senior manager'' hung up on me.
THIS IS A SCAM!