Virus on my calendar

1. Go to the Home screen, tap the Calendar icon, and select the Calendars tab at the bottom.
2. Spot the malicious calendar in the subsection called “On My iPhone”. The unwanted entry will usually have an icon whose color and design resembles those of the annoying events you’ve been seeing in the Calendar app.
3. Tap the “i” button next to the rogue entry, select the “Delete Calendar” option, and confirm the removal.

If you are using an older version of iOS, then the process of eliminating the dodgy calendar is as follows:

1. Tap Settings in the Home screen and select Passwords & Accounts.
2. Under the subsection called Accounts, find an unfamiliar account whose access permissions include, among other things, the “Calendars” feature. Its name may be “Subscribed Calendars”, “Other Calendars”, or similar.
3. Select the unwanted account and tap the “Delete Account” button at the bottom.

[Link Edited by Moderator]

Follow the advice posted by Axel Foley, in Calendar spam - Apple Community