kardotim on "Check to make sure we have premium package."

That's correct. Your bundle upgrade won't expire until 2013-09-27

Note that we don't allow plugins on WordPress.com for security reasons. Plugins are a feature only available for self-hosted blogs provided through WordPress.org.

However, you can easily add a Google Calendar by following the steps in this guide: http://en.support.wordpress.com/google-calendar/