Why anyone would to this in response to an automated overdue notice I'll never understand. I would presume, probably incorrectly, that Quickbooks generates these much like any other I've ever received with a line to the effect, "If payment has already been remitted please disregard this notice."
I don't care if it has that proviso or not, if I've sent something and get a late notice very near to the due date I presume that it either arrived slightly late or that it's sitting in the "to be processed" pile in accounts receivable.