Spam in my calendar

If you go to Calendars at the bottom of the screen there, do you see a calendar listed that matches the color of these events? If you see a strange calendar there under Other or Subscribed, can you uncheck it? Then you may want to check, it seems they get will add a strange mail account. Go to Settings>Passwords & Accounts and see if you find a strange email account there. It may be where the calendar syncing is coming from. Delete the account from there. You will also want to check Settings>General>Profiles, and see if there is anything unusual listed there.