You can't really stop them anymore. I've been in the communication business mostly setting up phone systems, VOIP systems & internet for businesses since 1987. There was a time the caller id number sent out had to be yours. Not anymore, I can program systems to send out any caller id number I want. I don't do this, but a lot of the telemarketers do this now. Any set of digits can be sent to get you to answer the phone. I get 10 a day myself, I missed a call today and it looked like a valid number so I called it and got the recording that the number was not in service. Also with rates so cheap lots of these companies are outside the U.S. dialing in. I talked with a bill collector who is based in Canada, but does most of his calling here in the U.S. I can set him up with a VOIP system from here and all of his calls in the U.S. are free, the calls across the street are international calls billed at $.03 a minute. You can plug a SIP phone into the internet pretty much anywhere that will log into your system provider anywhere. It's really cool stuff for legitimate businesses.
If you have success stopping the calls let us know.