How can I file a formal complaint

I closed my Fios account in June when I moved out of my apartment. Was assured that I owed nothing on the account and that I did not have to return equipment (I had purchased it). Then I got a bill in July. Called July 28 and the agent on the line found that there was a problem, apologized profusely, send me 2 emails confirming the closing of my account and of the autopay. Person said I needed to wait until the August bill for the charges to disappear. IMPORTANT: The persons said they had made a clear note in the record or my account regarding this error made by Verizon. When the August bill came, the charges were still there. To make things worse I received an email threatening to report my "debt" to credit reporting agencies. Tried, unsuccessfully, to reach someone by phone. Reached an agent via chat but I would not receive 60% of the chats the agent was writing. I could see they were typing but the responses would sometimes reach me and at other times would not. Ended that chat and started a new one. After a lot of back and forth the person said they could not solve the problem and asked me to call the Finance department. I decided to pay the bill and make a formal complaint instead but I cannot find a link or an email address to make it. If I go directly to Better Business Bureau they will surely ask me if I lodged a formal complaint with the company (Verizon Fios) first. I appreciate any help anyone can give me.

Re: How can I file a formal complaint

Hi JorgeL,

Your issue has been escalated to a Verizon agent. Please check your Private Messenger Inbox for a message from a Verizon Support agent. You can find your Inbox by clicking on your username at the top right corner of this page and then clicking the envelope icon that appears at the top of the menu. Response times may vary. Please continue to check your Inbox for a reply from a Verizon agent. Please direct all correspondence concerning your issue to the agents who will be assisting you privately.