I don't answer; and they don't leave messages.

called late very late at night. The day before, someone called from 1-613-236-6248 also again.

613-236-1744 an Ottawa area number, (and also 855-874-7480) in a recorded message said Revenue Canada has a 'criminal investigation' against you (not mentioning any name or who it is against, right there showing it's a scam). Then to call them back. A fraud scam it is, do not send them money.

I had a message that Revenue Canada has opened a file against me for fraudulent taxes???  Not sure hat that is about but it was a recorded message

It's a scam. These people try to pretend that they are from revenue Canada. Do not call them back and especially don't send the money or give them your credit card information. Block them if you can. They are wasted pieces of skin.