Erroneous Appointment Reminder

A client received two text reminders, the first on at 11:58am, the 2nd yesterday at 6:03pm confirming an appointment with me for May 5th at 6:00PM PDT.

Unfortunately the client was/is not on my calendar for the confirmed appointment, therefore I was unable to see him due to a reoccurring appointment I have every Tuesday at 6pm PDT.

Fortunately the client called prior to the appointment time for a different reason and did not show up to the office to be turned away.  I understand no system is flawless and glitches happen.  I am hoping this is not a frequent issue as I really am enjoying my trial period of Simple Practice and the reminder feature.  Please advise.