How do I delete an old CalDAV account from iPhone that no longer exists?

Question

A few months ago I tried to set up synching between my work calendar (via a CalDAV account) on my work Macbook, my iPhone and my home iMac. I never could get the account to set up in iCal on my iMac but it worked fine on my work Macbook and my iPhone. But we eventually went to using Google Apps, so now I don't need it.
The problem is that despite having removed the account entirely on my work Macbook's iCal, the calendar remains on my iPhone and keeps notifying me of reminders that had been set up there. When I go into my iPhone's settings, into Mail, Calendars, etc., the calendar is not there anymore (because I removed it when we got rid of using it at work) so I can't delete it.
I thought maybe somehow it was still hanging around on my home iMac, despite never having been able to set it up to work, but it's not there, either. The only place it exists is when I open iCal on my iPhone, although there's no way for me to delete it and when the notifications pop up I can't edit them, either.
Am I just out of luck here and stuck with this rogue calendar? When I plug my iPhone into my home iMac, where it's set up to sync, it tells me that my calendars are being synched over the air, not through iTunes. But when I go into system settings on that computer and force it to resync calendars, it doesn't get rid of the old CalDAV account on my phone.
Any ideas?? I'm stumped.

Answer 1

If your device is signed into an old ID of yours that is an earlier version of the ID you want to sign in with, do the following:
If you are using iMessage and FaceTime, make sure you are signed into these services with your current ID.  If they are signed into the old ID, go to Settings>Messages>Send & Receive and Settings>FaceTime, tap the ID, sign out, then sign back in with your current ID.
Then temporarily recreate the old ID by going to https://appleid.apple.com, click Manage my Apple ID and sign in with your current iCloud ID.  Click edit next to the primary email account, change it back to your old email address and save the change.  (You should not have to verify the old email account so it doesn’t matter if you no longer have access to it.)  Now go to Settings>iCloud, turn off Find My iDevice and enter your current password when prompted (even though it prompts you for the password for your old ID).  Then save any photo stream photos that you wish to keep to your camera roll (unless you are using iCloud Photo Library).  When finished go to Settings>iCloud, tap Sign Out (or Delete Account if you are not running iOS 8) and choose Delete from My iDevice when prompted (your iCloud data will still be in iCloud).  Next, go back to https://appleid.apple.com and change your primary email address back to the way it was.  Now you can go to Settings>iCloud and sign back in with your current iCloud ID and password (your data will download back to your device).