The same EXACT thing happened to me. I purchased a house and my phone number used to belong to someone who did not pay their bills. They called for years..
Unfortunately, I was forced to figure out what my rights were, and on the last conversation, I can not remember what I said, but something to the effect that they are violating such and such a law, and they stopped.
I am figuring out that most collection agencies out there are illegal. If everyone knew what their rights were and took the time to SUE, more collection agencies would be owing rather than collecting.
I am learning that the collection agency law firms, seem to be the only real legit companies that actually follow through with law suits,e tc.. and are interestd in collecting the debt.