What does it mean when my student loans have a zero balance due to a claim?

My student loans are through NelNet and I received a letter from NelNet instructing me to stop making payments. The reason they give is that my student loan account has been paid by a claim and now has a zero balance. I have had student loans since 1995; but I also have filed bankruptcy. What does all this mean? What claim paid my loans off? Did I or someone else get sued for the money?

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