Sadly, there isn't a whole lot that can be done. I suspect that many of these telemarketers are located overseas...beyond the reach of our law.
On a few occasions, I've received calls on my landline where my own telephone number is being passed along as a part of the Caller ID data stream. I called Verizon Core (Ma Bell) to see if they could do anything, but, they could not.
My guess is that the telemarketers are using some sort of VoIP service to make their calls and their equipment is changing the originating telephone number being passed along with Caller ID.