There are a few really good articles on how people are dealing with the recent influx of spam iCloud Calendar invites so I won't go over old ground but I did find another way that worked (so far!) for me.
Rather than creating a new 'spam' Calendar I decided to try a different approach.
What I did was to completely remove the iCloud Calendar from my local iOS devices and then re-enable them.
To do this
- DO NOT Accept, Decline or Ignore the invite
- Go to SETTINGS
- Go to iCloud
- Tap the switch next to Calendars, let it delete from your iPhone/iPad
- Once it's deleted your local device go back into SETTINGS-->iCloud and then switch the Calendars back on
I really hope that Apple addresses this quickly as I'm seeing more and more reports each day of this.