This number is from the American Lung [***]'n and as a charity, they are exempt from the Do Not Call list. It is probably dialed by a computer and then turned over to someone in a boiler room. If it doesn't get turned over to a worker quickly enough, it will appear there is no one there.
They called and said- You have a lead from Homes.com. Please hold for us to make the connection0 then it rang and rang. Sounded like a fax machine ring
call number and wait for prompt then remove your number . after that just call and wait for introductory to get to the part we are sorry then hang up , repeat as nessessary till frustration eases away . i will repeat tomorrow