Office 365 calendars not showing

I'm running Version 8.0 (2032.6.1) of iCal on Yosemite. My main calendar is hosted on Office 365.

There was a problem with duplicated entries in the calendar, which actually meant that iCal would crash on startup. I fixed that by deleting the duplicates with temporary access to the Windows version of Outlook. As part of trying to get iCal to work again, after the repair of the calendar, I removed the various caches and .plist files, as recommended on various sites. Now, I'm in a slightly strange state in that the Exchange (Office 365) account isn't listed in the iCal list of accounts, and entries for that calendar are not showing, it is still in some way connected, because the application icon shows the number of outstanding entries.

What is the best way of restoring visibility of the Office 365 calendar in iCal?

I've tried deleting and re-adding this account, but it hasn't helped.