I just read some literature provided by a credit repair advice company (which I found on eBay) and they recommend sending GW letters to the President of the company. If that doesn't work, they said send it to the CEO, and if that doesn't work, send it to the whole board of directors. The idea is to let them know that you are not going to go away.
They said you can find out who and where that is by looking up their SEC filings online (haven't tried it yet, but sounds promising).
I had a couple little tiffs with AT&T and Washington Mutual a couple years back and I got results both times by writing to the President, but I also had a really good legal argument on my side.