Getting event notifications for calendar I'm no longer subscribed to

Since updating to iOS 6, my iPhone has been giving me reminder notifications (with sound) for a calendar that I'm no longer subscribed to (a Meetup calendar). The events don't show up in iCal or my iPhone Calendar app, just when the notification happens... and when I swipe to look at the notification, it says it's from "untitled calendar". I can delete the event at that time, after the notification alert, but that's not helpful.

I've looked in iCloud and on my phone's settings, but I can't find this "untitled calendar" anywhere and so can't delete it or the ghost events.