Virus in my calendar

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

If running iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Any rogue entries here? If so, delete the rogue account. 

If running iOS 14, check: Settings - Calendar - Accounts - Any rogue entries here? If so, delete the rogue account. 

You’re welcome. It’s almost impossible for an iPhone to be infected with a virus or other serious malware. To put your mind at ease see→Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support