You stated that you've been working with them for 'a few weeks now' and I wanted to offer up my own personal experience.
I sent a DV letter in November 2007 and received a response from the CA in about 30 days. That's pretty typical.
I responded with a letter outlining my terms and conditions for settling the debt as 'Payment for Deletion' and I added something else to the end of that statement; not negotiable.
I sent the same letter (with a current date) over and over and over again for 8 months.
After some back and forth with them through the US Mail system for the 8 months (yes, it will take a while for them to finally crack), the CA gave up and deleted their trade line from all three credit reports.
Bottom line is I did not compromise with them and was not going to take no for an answer. The best advice I can give anyone is generate a professional letter stating your position and keep hammering away at them.
The end result is my credit scores (FICO) increased over 80 points just by having that one and only negative trade line deleted. It's worth the effort and the patience to stick it out.
As the most decorated Marine in US History ('Chesty' Puller) once said, "Hit hard, hit fast and hit often".
In my case, it worked.