How to file a customer service complain? Need to escalate the issue to higher management

I returned the TV box in Feb last year(2017).  I called the CS last year in March and they said the will take care the issue.  However, they did nothing until I called again this year(2018) in Feb.  Finally they took the box off my account.  It's really furstrateding that I have to call the CS for 5 times within a month to take care this issue.  However the CS told me, she can't refund me the 11 monthes that they over charged me for box fee.  The most they can do to credit me 3 monthes fee.  She even said it's my fault not to follow up after I reported the issue last year and let verzion to over charged me for an year.   OMG.  I found this is hard to beleive.   I have UPS traking # and proof that Verzon received the box in Feb 2017.   I asked the CS to speak to the supervisor, she said she is the supervisor.   I would like to know does Verzion has the complain deparment?  Or I should just file my case to BBB.   Thanks