There could be some very pretty big consequences to this screw up. It would seem the a prompt message of explanation might be a good idea. But it’s a teleco, so that would seem unlikely.
While it's likely explained by other commenters as a possible replay of previously sent messages, AFAIK there is no SLA for the guaranteed windows of SMS delivery.
Also, "pretty big consequences" rarely apply when you enter into a "binding arbitration" clause with your cell phone provider.
