I am paying on a commercial student loan that went into default.
What do you mean by a commercial student loan? Never heard of this term. They are either private or federal. Here's the issue the collection agency through which I am paying keeps sending bills showing no decrease in the debt or indication that I am paying the debt. I am paying 100 per month. The loan is for 3000. Assuming 9 percent interest (my state's right for settlements- that would mean at 1200 for the first year- that should be a decrease in 2 months of the debt to roughly 900 bucks). I have had problems talking to them because they refuse to negotiate.
Collection fees and any past due interest are paid first, and then principal. What are you trying to negotiate? You have a prom note with all the terms outlined...they do not have to negoatiate. Again it would help if you posted what type of loan this is and who the holder/guarantor isThe agency has already engaged in a couple questionable practices that I let go because I wanted to pay off the debt, but now, that I see they are not decreasing the bill on their record to me- I am concerned.
Here are my questions: a) Are they taking the money, but not crediting it toward the debt?

Can they be charging me collection fees rather than crediting the money toward the debt? Is this why they refuse to negotiate?
CA's dont charge collection fees...your loan holder/guarantor doesc) Finally, should I take them to court to obtain some sort of settlement arrangment? I have explained to them that I am paying the maximum that I can afford given my other debts for which I am trying to remain in good standing. They still refuse to negotiate, and, indeed, one woman hung up on me. At first, I thought- maybe they want to see that I am acting in good faith. But it's been 10 and half months. They claim their client does not want to come to payment arrangment unless I pay a lot more per month or pay off in full.
You need to do some serious reading on student loans. You are in default and you basically gave up all your rights...you signed a prom note agreeing to balance in full on demand upon default. If you took a private loan to court, they would turn around and file judgement against you and win.