Verizon Wirelesss Audacious $500 charge for broken phone Internet

So as we all know Verizon bought out Alltel. I had the Blackberry World Edition under Alltel contract and the trackball for this phone stopped working and I could not work the phone at all. I went to file an insurance claim only to find out that Alltel had been bought out by Verizon.

We switched from Alltel to Verizon and I got the Blackberry storm. I had kept the Alltel Blackerry because I had figured that since Alltel didn't really exist anymore there was no need to send it in. WRONG!!! Verizon slapped a $500 charge to the cell phone bill without an explaination of where it came from.

Called Verizon to figure out where the charge came from and they said that it was because of the Alltel Blackberry that I had. They said that if I sent it in the charge would be taken off of the account. So I of course immediately sent it in.

The charge is still there and they are claiming to not be able to find the phone. So not only did I pay the $90 for the replacement phone, they are also getting me for $500 dollars on a phone that did not work even if it was still in my possession.

I have given them the date in which I sent  it out. I have people who were with me when I sent it out but the $500 is still on my account. Is there anything that I can do? The phone wasn't even $500 to begin with and especially not when it doesn't work.

Advice? Please?