Unggggg!!! Believe it or not, we've had our current phone number for almost 12 years, and we STILL get some of these calls from collection agencies looking for the deadbeats who had the number before us. Some collection agencies just don't give up--ever.
I didn't even know him, and the agency's attitude was "get your neighbor to pay, or pay it yourself, and we'll stop calling."
After 3 calls, I told them that I was filing a complaint with the FTC (I had asked them the name and address where they wanted the money sent).
No more calls after that.
I had a collection agency after me once - for a charge I'd paid up front and by credit card. They likely knew I didn't owe the money but were undeterred. They harrassed me for years and until I harrassed them back.
I kept calling the person who called me until they disconnected that line. Then I called them on other lines, over and over as they kept hanging up on me. The last guy I kept calling was completely flustered. They stopped calling.