The person receiving the calls needs to get as much information about the company calling as possible, they could even do it under the pretext of being helpful. If they have caller ID, record the number that shows up there. Then ask the person calling what organization they represent, company name and address, get a phone number etc., if they balk, just say "I'm not going to help you unless I know who you are". Then ask them specifically what it is about, what the debt is, how much etc. try to get them to give you as much info as possible
Then explain that the person they are trying to contact does not live there and has not lived there for years and that they aren't going to pass along the information and that they are to stop calling at once. And furthermore, sharing information about someone else's debt is a violation of Fair Debt Collection Practices Act, as is making harassing phone calls etc. and if any further phone calls are received a complaint will be filed.
If it continues file a complaint with the FTC under the Fair Debt Collection Practices Act, 15 U.S.C. 1601, et. seq. Section 806 of the FDCPA prohibits "any conduct the natural consequence of which is to harass, oppress, or abuse any person in connection with the collection of a debt." The "any person" and "in connection with" parts are interpreted pretty broadly, and you don't have to be the "consumer," i.e., the individual holding the debt, to be protect by section 806. Specifially included as a violation of that section is "[c]ausing a telephone to ring or engaging any person in telephone conversation repeatedly or continuously with intent to annoy, abuse, or harass any person at the called number
The complaint can be filed on-line at:
https://www.ftccomplaintassistant.gov/