Palisades Collection Agency

This agency has been harassing me for a couple of years. The first time they sent me a notice that I owed over $100 to Verizon. Although I never received any such notice from Verizon I sent a check to Palisades. Now, a year or so later, they are trying to collect from me again for a debt they say I owe to Verizon. This time I called Verizon (they are no longer my phone carrier) and they verified that I do not now, nor have I ever owed them any overdue payments. I sent Palisades a Cease and Desist letter but they are now calling my home very day. Can you help?