Hathway — Device return threatening

Today I received mail from hathway for return of modem, after several month of deactivation request. I was in a rented house and shifted to new location. I am not even sure if modem is still there and more over I paid full advance for modem and they have no rights to ask for a return after 1 year of connection. and I am receiving 3 calls on daily basis for renewal and return of modem. I never had this kind of service from any product from my childhood. such a worst company i ever seen. I would rather beg in street than doing this kind of things for money looting.