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We can delete the Google account and add it back. This will re-sync the calendars. Go to Settings > Mail, Contacts, Calendar. Tap your Google account and remove it. Then add it back from there by tapping Add Account.
When adding, you will get an option to turn on Calendar, Mail, Contacts etc. Turn them all on. This should re-sync with Google calendar.
If that didn't work, then go to Go to Settings → Mail, Contacts, Calendars
Restart your iPhone and check Calendar. Please let me know if that didn't work, so we can continue troubleshooting
If the above options doesn't work, then try this solution.
That should do it. If it still not working, then open App Store. Search Google Calendar and install that app. Open Google Calendar and sign in to your Google account. Do you see your calendars there ?