Is the calendar you subscribed to available in Settings?
- Select Settings
- Select Calendar (or Mail, Contacts, Calendars in iOS9 and below)
- At the bottom of Accounts section select Subscribed Calendars
- Turn OFF Use SSL
- Toggle Account OFF and ON again
- Go back one step to Mail, Contacts, Calendars
- At Fetch New Data turn ON Push
- Set all calendar subscriptions to Fetch
- Select Every 15 Minutes for Fetch New Data
If not available
Please order the calendar again, Apple will recognize if you already purchased it and won't charge you twice.