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Tell them you do not want your debt to 'be forgiven', you want to make good on your obligation and you are not going to take no for an answer - basically tell them to "shut up and take my money". They can send you a corrected 1099 if one has already been sent.
The problem with the 1099 thing is that often banks will NOT zero the reported balance even though the debt has been forgiven. I believe Cap One and BoA are a couple of ones that are notorious for this.
You would have to get your limits above 25K for it to have a really beneficial effect, and I don't really see that happening with 600 scores....