I get calls for people who have never lived at this address but I guess may have had this number (but not for at least 9 years). I have also gotten calls for relatives with completely different names. The only thing I can figure is 1. they have me linked to their names because I grew up in their home and then they cross reference and get my number or 2. at some point they have listed me on some application as a reference or family member.
I don't like to lie to anyone so I answer "I'm sorry but you have the wrong number". The next question is almost always "Do you know them?". I don't like to lie but when I say yes, they ask me for their number. Well, this particular family member has an unlisted telephone number but has had the same number since before I was born (I am almost 39). If they have legitimate business with them, then they already have their number. If not, I am not giving it. Also, if I become their messenger then the calls will never stop. So, I say "yes I know them but they have an unlisted number. Please take my number off your list".
I have then passed the info to my relative that someone from that number called. Only because of who this relative is.
They are trying for one or more of the following to happen...1 catch up to the debtor, 2. reach a friend or relative who will get them in contact with the debtor, or like you said 3. get pressure on the debtor to get the calls to stop.
Once you notify them that they have the wrong number, they are obligated to take your number out of their system for the debtor. You probably have to allow processing time but after that, I believe the calls would be against the law.