I had a similar situation a couple years back-them calling from about 3 or 4 numbers daily. I rounded the numbers up and found someone in the local office who cared enough to help me and the next day the calls stopped.
Don't answer. That will mean more calls.
Why do you think they hang up? All they want is a working number which you tell them when you answer.
If machine gets it they hang up
They are crooks. Just don't answer
Calls from 202 area code: 650-6149 - WINDSTREAM Landline in Hyattsville MD
770-2489 - BANDWITH.com VolP in Washington DC
770-2406 - ALA in Washington DC
Sometimes I answer but do not say a word - no message is left and soon they hang up but always call back!!!!