Many of these collection agencies that do the robo calling simply have a giant list of names and phone numbers and money supposedly owed. These debts could have been turned over 3 or 4 times by the time these agencies start calling you. All they have is a list, no documents or background.
As an alleged debtor under the fair debt collection practices act you have the right to demand a validation of your debt. From my experience, when you demand a validation of the debt, the agencies stop calling.
You also may have some legal recourse for the harrassing phone calls, but I have personally found it difficult to obtain the necessary documentation. When a collection agency robo-harrassed me, they probably called me 30+ times but I never picked up my cell phone. When I was considering legal recourse I could not obtain any documentation from my cell phone provider that these calls were made. My cell phone provider only keeps a record of phone calls which are picked up.