My iPhone might be hack by someone

That is a Rogue Calendar account. Go to Settings-->>Passwords & Accounts and under Accounts see if an unknown calendar account is listed. If it is then tap on it and then Delete account.

Note that it is not a virus. It is something that got added to your calendar because you may have accepted an offer from a pop-up  on a website unknowingly. Please be careful out there,

Good Luck.

Axel F

Your calendar may be linked to your iCloud, and somebody may be using your iCloud to put things into your calendar through that. Log in to your iCloud account at https://www.icloud.com, and check "Devices", see if you have any other devices inside your iCloud account that you do not recognize, and remove them immediately. I would also recommend you to change an iCloud password if you find an unknown device in your iCloud.

Hope this helps!

Apple just released this article yesterday, it probably can solve your problem too: https://support.apple.com/en-us/HT211076