I don’t know if you can do much legally. Do you have any proof that you contacted the ISP and asked them to take your name off the records? Do you have the name of the person you talked to? Times/dates that you called? Anything will help at this point, but you may still end up being stuck with the bill. Call the ISP and talk to the highest person in command you can. I’ve disputed bills three times, and I’ve defeated bank late charges, American Airlines and AT&T. The secret is to bypass the low-level customer service people and bitch, bitch, bitch. But bitch in a professional way. I was once promised compensation for lost luggage with American Airlines, but due to a number of muck-ups on their part, never got it and then my name mysteriously disappeared from their computers and there was no record of me being entitled any compensation. Did this stop me? No. I found the name of the vice-president of operations, wrote him personally, enclosed a copy of the letter to the proper customer service department. The VP contacted me directly by e-mail, apologized, refunded the money promised and gave me two free tickets. I had no proof of anything. Just my word and all the supporting documentation I could find, which didn’t amount to anything promising me in writing money. But I wrote who I talked to, when, and the exact sequence of events that prevented me from getting my money. A few months later I myseteriously received ANOTHER check for the amount owed to me.
With AT&T, I had no leg to stand on. I got a bill for $300 in int’l calls that I made. When my roommate moved out and switched the phone to my name, I forgot to request that the int’l calling plan be preserved on the new account. Or something like that. The cost savings were the difference in paying $1.35/min to $0.25 a minute! The customer service person couldn’t help me, said she couldn’t backdate the bill. I said “bullshit, I’ve had 'em backdated before,” she said “No, I can only put you on this plan now.” I said “Well then, let me speak to somebody who has the power to do something.” Five minutes later, my bill was reduced to $75.
Bank One, same thing. I got charged over $100 in late fees because I didn’t get my mail. Customer service did nothing for me. I finally asked to talk to some high-level employee (it helped that his name was given to me by a friend). Late charges, erased.
I’d advise you to try to do the same thing. Don’t talk to the highest person in charge, but somebody just below. Explain the situation clearly and fairly, and with luck he or she may be able to help you. Explain your position as a loyal customer, threaten never using their ISP again if need be (in as friendly a manner as possible, like “I’m sorry, but I’ve acted in good faith, and if we can’t resolve this situation, then I cannot be expected to use your services in the future.” Ya know, that spiel.)
I’ve found that big companies do try to be helpful to their customers, as long as you talk to the right people. Just make sure that $120 doesn’t go to collections.