I used a 3rd party data transfer tool, called "Smart Transfer".
It worked fine, transferring apps and other stuff to my old phone.
However, I had chosen to transfer my Calendar. Bad move.
This added, SmartIO accounts to my Calendar.
1. Open Settings
2. Go to Apps
3. See all ... apps
4. Three dots, top right
5. Show system
6. Select, Calendar Storage
7. Select, Storage
8. Clear, Storage & Cache
Solved! Go to Solution.
Thanks for the word of advice, Protonumus.