I got hacked

You have NOT been hacked, but you DID at one point click on a link which downloaded a calendar to your phone. You did this yourself, though you likely were not aware you did it. It's often unwise to click on links unless you know the source well.

To get rid of this, go to Settings > Passwords & Accounts

Check the accounts section below and look for a calendar you didn't know you downloaded and delete it.

Because, it is not a hack. You subscribed to a bogus calendar, that’s it. Delete the calendar as directed above and move on with your day.

You subscribed to a bogus calendar. Read here: https://support.apple.com/en-us/HT211076

~Lyssa

You’re welcome.

For future reference, see: Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support