I had a similar experience last year they charged me  a early termination fee for a phone i had already paid off. I battled for 7 months to find a Tech  that Knew just what to do and how to fix the issue.
I had them offer me  a small credit and i had them tell me i had to pay the bill THEN they would credit that to my account.
I spoke with FTC an BBB and discovered that i should NOT pay and that they need to fix the issue. As i said i finally got a great tech who worked hard to fix the issue.

I have had my bad share of CSR and Techs who sadly were more interested in reading from a cue card and not really assisting anyone or possibly just not aware of how to fix the situation and i believe that is poor  training. All that said i have had some Really Wonderful CSR's and Techs too who have worked t get my account fixed or phone back on par etc,
If you get lucky enough to get one of them you will find thy make Verizon worthwhile

Mind you i do not work for Verizon or any parts of it i simply have had their service for several years and most times i am very happy