"Duct Cleaning Service". Want to bet it is a spoofed number?

I keep getting calls from the same "Air Duct Cleaning" Services, every day.
Not sure if it's the same caller, but it sounds like a younger individual, probably from or around India.
Asked them nicely to remove me from the call list.
I've cursed at telemarketer.
Hung-up as soon as i heard the company name, dragged conversations to waste their time.  
But they still keep calling, every day.

Jack, of course it's a spoofed number.  The ring is long distance but the area code is local.

This is how I'm getting even, and it's driving them crazy. When you hear the dead air after saying Hello......block the mouthpiece with your thumb and listen to the idiot say Hello 25 times ...he then hangs up thinking his phone is screwed ....great entertainment and all free......

Third world Pakistani or Indian call centre. Don't even bother to answer if you have Call Display. If you have an answering machine, let the machine handle the call. If you do not have Call Display, and they ask about "Duck Cleaning", let them know you have no "ducks" to clean. Instead, tell them you have a cow you wanted cleaned so that you can later barbeque the cow and have some nice meat steaks. They will be totally unable to handle the reply as cows as deemed sacred in their culture and they would never consider eating any type of meat product, especially from a "sacred animal" as the cow.