So the mystery of the creepy phone messages about an important customer issue is marginally solved.
Today, it was a different message, though I'm pretty sure the number to call was the same; but the message was preceded by "Michael Dunham," did not involve a teenaged voice saying, "Again, I repe-eat," and actually included a case reference number along with the phone number. Thus, the calls are for someone who evidently used to have my phone number. I've gotten calls for this Michael Dunham before from businesses, and once for a particularly human sounding message I called them back to tell them they're barking up the wrong tree. It's only a matter of time before I call back this time and beg them to quit hounding my phone.