I received a check for $861.85 out of nowhere.

Sir: I just wanted to tell you about what happened to me on 10-01-2018. I received a check for $861.85 out of nowhere. The letter stated that I was overcharged in interest from a loan that I got some time ago and this was my share of the settlement. What makes this so surprising is that I have not even gone through all the stuff I received from you.