Verizon Fios Charging me for service after I cancel and returned their equipment Maryland New York

Verizon is charging me for a new service after I returned their equipment and cancel their service. I spoke to several representatives but they keep telling me that I signed up for another account. Another representative told me that I did not call them to cancel my service and returning my equipments and stating that I am closing my account does not guarantee that my account is closed. 

I believe that they have realized that customers are cancelling their services at a higher rate and they have device a new way to continue billing customers. When you call them to cancel services they keep transferring your call until it gets disconnected. Please help us to prevent them from charging the customers unnecessary fees after they switch to another provider. 

Thank you.