Verizon Wirless Please check your bills! Internet, Pennsylvania

I recently became aware that Verizon Wireless has been over charging us for at least the past 5 years.  The store and customer service both acknowledged that we were to be getting an 18% discount instead of the 8% that was on my bill. I was then given a series of tasks to complete to get my money back and then only offered 6mths worth of what is owed to me instead of the full five years they overcharged me. I told them it was completely unacceptable. I talked to customer service once, where they told me even though they acknowledged we were entitled to that discount I needed to call back with proof.  The number she gave me was no longer in service and I had to fine a new number to call.  The customer service rep kept offering me 6mths back instead of the full amount, kept putting me on hold, and only after I threatened to use my lawyer and report the Better Business Authority he let me talk to his supervisor.  Currently his supervisor is "researching the issue, but kept offering me six months of my discount". He claims he is going to call me back with in 48 to 72 hours. Though with my previous experience  I doubt it.