Account Control Technology Tapping, Stalking, Tracking Mason, Ohio

Today I was contacted by Alicia with ACT. She was looking for my several years estranged sister. I have no information. After hanging up, I thought of something. I am at a friend's house. This address and phone number has never been listed as mine, so how would ACT know to contact me here? They aren't relatives or anyone that could be traced to me by official means.

I called back, Alicia could not answer my questions, so I asked for her supervisor. I asked the supervisor about it. He said they get information from 'vendors'. I know some companies sell information, but I have never used this address or phone number, so why would the vendor even have it? On only a couple occasions I have used this as an alternate phone number, but that was with employers since I was on call. I also asked what business ACT is in. The supervisor refused to tell me. He said to Google it. When I did, that's when I learned that they are a college loan collection agency with numerous complaints on Ripoff Report. I am sure I have the right one because the phone number I was called from matches the one listed on one of the complaints here.

Here is my concern: I cannot think of any legal or official way that ACT would have known to contact me at my friend's house. What are they doing? Tapping lines of debtors' family to see who they call and harvest phone numbers? Following relatives of people they are attempting to collect from? I hate to sound like a conspiracy theorist, but that's the only explanation I can think of.