Verizon trying to swindle $300+ in repair costs Weldon Spring Missouri

In July 2007, when I moved to my new apartment, I found that my existing Verizon DSL (that I had asked Verizon to reassign to my new place) wasn't working there. I contacted Verizon support and they sent down a repair man, he told me that my phone jack box was busted and he installed a new jack box. But a few weeks later I received a bill for around $330 for that one jack-box. It should be noted that at no point did the repair-man tell me that it will cost me, and neither did he ask for my permission before doing such costly repairs. I immediately called Verizon HQ and disputed that ridiculous charge (for crying out loud, I could have gotten an year's worth of DSL with $330 through any other ISP) - they agreed with me on the phone but told me that the local Verizon office is the one who did the installation and they alone can cancel that charge. After bugging the local Verizon office over the next couple of weeks (turned away everytime with the excuse that they need to run it by their supervisor), I was finally told that they will correct that charge. I assumed it was all taken care of at this point.

However, when I pulled my credit report a few days ago (I hadn't checked my credit report since then - I was a student before now and didn't really pay much attention to my credit report), I found that this charge was still there, infact with late fees and penalties it has now risen up to $614 and is showing up as 'charged off'. I have spent the past few days on the phone arguing with Verizon about this, but they claim that their computers don't show me as owing them any money and that they never charged me this $330 for repairs. I don't want to call the collection-agency number listed on my credit report as I am afraid they will use my call as an excuse to re-open my account. Can anyone tell me what should I do at this point?

Ali
Ithaca, New York
U.S.A.