I just found out about this after having VZ for two years. I'm sure they owe me tons of money due to this. I've already told them to cancel my international service, but now I'm going to send a major complaint letter, as well as cc letter to whomever I can figure out needs to know about this. It's double-dipping. A class action should be brought against them for this.
You can get your minutes here: http://www22.verizon.com/foryourhome/MyAccount/ngen/pr/svcs/phone.aspx?type=classic.
But that doesn't mean it's right. So bottom line: it doesn't look there's really a way to find how many minutes you actually used.
Even customer service can't help. The only thing they told me was that "it looks like there's an overlap, because my billing cycle begins on the 7th, but calls from the 7th are on the prior month's bill".
Something wrong here.