Typically, if you feel vzw (or any carrier) has overbilled you, this will not be a valid waiver for an early termination fee. In what way did they overbill you? How did it go for several months?

I pulled this off of the web site:
How We Calculate Your Bill
Your bill reflects the fees and charges in effect under your calling plan at the time they're incurred. You can dispute your bill, but only within 180 days of receiving it. You must still pay any disputed charges until the dispute is resolved. Charges may vary depending on where your wireless phone is when a call starts. If a charge depends on an amount of time used, we'll round up any fraction of a minute to the next full minute. Time starts when you first press SEND or the call con...
(continues)

you're going to have to elaborate.

verizon "overbilled" you? was it a billing error or did you just go over your minutes? if it was a billing error, they should just fix the error, not credit your ETF. if you went over your minutes, verizon should charge you double....