The infamous Duct (Duck) Cleaner Scam. The number they use is "spoofed" and you will not be able to return their call. The number appears to be non existent and "cannot be completed as dialed".

Here is what I do. If they ask if you want your "ducks" cleaned, tell them you don't have ducts in your home. You are completely ductless as you use radiant floor heating instead. Tell them you have geese, cows or which ever animal you prefer to have "cleaned". I ask them if they clean geese. There was silence on the other end of the phone, I asked again if they clean geese, and he finally answered that they did not and even apologized for calling :)

I don't get upset with them and I play their game when call. After that, I reported the spoofed number to the CRTC.