Hi, I have received a message which says I have virus in my phone and it has been hacked

Hi

This is calendar spam, not a virus. And you have not been hacked. You have just authorised a web page to install a calendar.

If you have iOS 13 or earlier versions, check: Settings - Passwords & Accounts - Accounts - Check for any accounts that you don't recognise - remove them if there are.

If you have iOS 14, check: Settings - Calendar - Accounts - Check for any accounts that you don't recognise - remove them if there are.

See:

Remove spam from Calendar on your iPhone:

https://support.apple.com/en-gb/HT211076

You allowed an app or website access to your calendar.

They filled it with spam.

Its not a virus.