Turns out my DA account has been hacked several times in the past few months. I've received messages from numerous people I've never messaged, ever. Apparently whomever broke in was pretending to be me. I'm not sure if someone is spoofing my account or has broken my password (which I've since changed to something very long and unique; I suggest the same to you all). In any event, if you got a message from my account, and then you wrote back to that message, and then "I" did not reply back ... or at some point I wrote something like: "I do not know you" ... that's why.