Events from deleted calendar(s) showing on calendar app (iOS), but not on iCloud web

I just switched to iPhone after being a life-long Android user. Surely I did something weird.

I used the Move to iPhone app and it added my google calendar accounts to my new phone. Seemed fine. However I was getting events multiple times; it seemed that I was getting notifications from each calendar account, and also from the default "Calendar" that was created by the Apple Calendar app.

I decided to just use the Google app for my calendar events (for now?), so I deleted the accounts from Calendar via settings, but those events from the now-deleted calendars/calendar accounts are still showing up on my default "Calendar" in the Calendar app and syncing; and worse, I'm seeing them in triple now.

I can't find a way to clear my calendar app; when I sign in to the iCloud web-version of the calendar, there are no events. I tried creating a calendar event there, and it did _not_ sync to my phone as I expected it to.

What I've tried:

• rebooting the phone
• deleting and re-installing the Calendar app
• disabling/enabling sync