How to delete events you didn't create (spam ads)

Your calendar account may be affected by spam.
Please review your calendar settings as follows.

If you use Google Calendar

1. Open Google Calendar on a computer
2. Click the gear icon at the top right and open "Settings"
3. Click "Event settings" in the list on the left
4. Set "Add invitations to my calendar" to "When I respond to the invitation in email" (or "Only if the sender is known")

If you use iCloud Calendar or another service

1. In Simple Calendar, open the details of the unwanted event
2. Check which calendar is shown under "Calendar Name" at the top
3. Open the Simple Calendar settings and tap "Add/Edit Calendar"
4. Tap the calendar you identified in step 2
5. Tap "Delete Calendar" (see the note below)

Note:
The calendar identified in step 2 is the one targeted by spam. Deleting it does more than remove a link: depending on the account, the calendar and all of its events may also be deleted from the synced account and from your other devices. If you only want to hide it, use "Display Settings" instead.

If neither method works

1. Open the "Settings" app on your device
2. Tap "Apps" → "Calendar" → "Calendar Accounts"
3. If an unknown account (such as "CLICK SUBSCRIBE") appears, tap it and delete it

Spam targeting iCloud calendars has increased in recent years. For more information, see the official Apple page:
How to delete calendars and remove events on your iPhone

Apple and Google actively fight spam. You can also protect yourself by using an email address that is hard to guess and by not tapping suspicious links.