My iPhone has been hacked

You got tricked into installing a rogue calendar; your phone does not have a virus.

If your phone has iOS 13 or earlier: Go to Settings/Passwords & Accounts, look under Subscribed Calendars, tap on the offending calendar and delete it.

If your phone has iOS 14: Go to Settings/Calendar/Accounts, Tap Subscribed Calendars, tap on the offending calendar and delete it.

And in the future beware of "free" offers

First step would be to describe the symptoms of your hacked phone so we can offer relevant advice.

Your phone has not been hacked. Why do you think it has been?

I am getting a reminder every hour on my calendar that there is a virus