Duct cleaning scam

Called today - Victoria Day in Canada - wanting to sell duct cleaning services.  I don't know if it's a scam, but I had to ask him three times which company he was calling on behalf of. He finally said, "Safe Home Services" which appears to be based in Ohio (not Ottawa, ON).  Then I asked him to put our number on the "Do Not Call list" and he hung up on me!

Yes it is Victoria Day here and we too have received two calls in two days  from this number.
However, no one speaks but you can tell the line is open.
We suspect the caller trying to see who is home and at what hours.
Maybe instead of duct cleaning, they want to clean us out of house and home.
Note: we too have reported this number to the do not call list.

Also, at other times with this number, we have heard some quite obscene messages.