1) find a lawyer who you can hire for an hour or two for $200-$400. You're paying for his letterhead, not his skills.
2) Get him to write a letter saying "you have 14 days to pay 2/3 of the amount. If we receive that, the debt is discharged in full. IF we don't receive that by 14 days from today, we're going to court, and we're asking for the full amount of the debt, lawyer fees, and damages. Please pay now."
I've collected LOTS of debts in my time, 95% successfully.
This technique works.