Found in Natural Language Calendar Won't Stay Deleted

I have a Mac Air with OS High Sierra 10.13.6 and an iPhone 8 w/iOS 11.4.1. I am using the Apple Contacts & Calendar apps on the Mac & iPhone.

Does anyone know how to PERMANENTLY delete the Found in Natural Language Calendar (FiNLC) from iPhone8? I have deleted it numerous times but it continues to return. This is a potential problem because it almost caused me to lose all of my historical calendar data.

I upgraded from iPhone 6 to iPhone 8 back in February. Somehow in the transition at AT&T, FiNLC became my default calendar with all my historical data. Since that calendar is not on my Mac, when I synced the new phone to my Mac, I lost all of my historical calendar data. Fortunately, all my data was still in the iPhone 6 backup so I was able to recover it.

I have disabled all of the following on my iPhone8:

In Settings, Calendar, Siri & Search:

Siri & Search Suggestions: Off

Show App: Off

Find Events in Other Apps: Off

I turned off all other calendars except “Calendar” which is the only one I use to enter events.

It still comes back!!