Folks, it isn't the duct cleaners who are calling, it is a telemarketing company who was hired by the duct cleaners. If you want the calls to stop you have to educate the duct cleaner about how expensive telemarketing is. That will cause them to stop using it as a marketing tactic.
1) Schedule the service call, But pay nothing over the phone.
2) file a do not call complaint with NC Attorney General and make note of your case number.
3) then when they arrive, get their company name off the truck and take a photo of their license plate. Be NICE but refuse to let them in tell them you couldn't get the telemarketing company to stop calling you and ask them who it is. Give the serviceman a piece of paper with the open DNC complaint case number and contact info for the NC State Attorney General Encourage them to have their boss call.
4) After they leave update your open case with the new information about the Company.
In a couple weeks you will get info from the state attorney general. Either the cleaners or the telemarketing companies will have to pay the state fine for violating the law.