Purchased Gateway Router from 3rd party still being charged Rental & Customer service issues

[Betz1]

I purchased a Verizon required Gateway Fios router from a Wholesaler and swtiched to it, returning Verizons modem from install. I have continued to be charged rental fees. After 3 calls with Support I was told that the modem is shown in their system as Verizon owned equipment still, from unreturned equipment or final bill not paid possibly. The account representative told me I would need to contact the previous owner to obtain a proof of purchase from Verizon so they could stop charging me the rental fee. 

Is that legal and how can Verizon hold a new customer liable for equipment from a previous customer? The agent supervisor also told me that they could not verify by serial number that the modem in question was purchased thus possibly making money from both myself and the previous customer. 

I am looking for answers and need Managment assistance to escalate and resolve this issue. The previous two associates did not tell me any of this information while I tried to resolve the issue and signed up for a 2 year contract. Only after asking to talk to a supervisor was this information explained to me. Once it was, within minutes of agreeing to the 2 year contract, I wanted to cancel the contract and was told "it's already been processed and I can't change it". Basically a big screw you! 

[LawrenceC]

Hi Betz,

Your issue has been escalated to a Verizon agent. Please check your Private Message Inbox for a message from Verizon_Support. You can find your Inbox by clicking on your username at the top right corner of this page. Please direct all correspondence concerning your issue to the agents who will be assisting you privately.