Unable to Remove Subscribed to Calendar from Calendar App

Model: iPhone 8+ (MQ992LL/A)

iOS Version: 11.4.1 (15G5072a)

I have a calendar that is showing up in my Calendar app that I would like to remove but am unable to do so. It is showing up under the "Other" calendars as "US Holidays" in my Calendar app as seen below:

When I click on this calendar's "i" option, there is no button to "unsubscribe" or "delete"...

After trying to remove it from my Calendar app, I went into "Settings -> Accounts & Passwords" to see what account the calendar might be associated with. I went through all of my accounts, individually deleting them on by one to see if the US Holiday calendar would disappear. Unfortunately even after deleting the various accounts calendars, the subscribed US Holiday calendar is still showing up.

Finally I went to the "Fetch New Data" section of the "Accounts & Passwords" settings and found two calendars in there that do not show up under my accounts. One is called "Holiday Calendar" and the other is called "Tyler Bond".

How do I identify what account these calendars are associated with and how do I go about removing them from my device? I have tried everything I can think of and yet they are still showing up on my phone...