One ring, no message. Didn't call back

I'm getting this number showing up on my iPhone as a "Call Back" notification in my reminders app. 3x today.
How is this possible? Their placing reminders in my personal reminders.app. What the......?

Rang once.  No message.

Called my cell. Did not answer. Left no message. Not calling it back.

One ring, hang up.  I think they are fishing.  I blacklisted them.