How to cancel my icloud plan

Read this support article about how to downgrade or cancel your iCloud+ storage plan on an Apple mobile device, a Mac, or a PC. --> Downgrade or cancel your iCloud+ plan - Apple Support

Hey there,

Even if you can’t access to your iPhone, You still can cancel the iCloud+ plan by using your Mac or your windows pc or any devices that you have signed in with your Apple ID Please follow the instructions on this article to learn how to do this :Downgrade or cancel your iCloud+ plan - Apple Support

All The Best!

You can also cancel subscriptions online. See: If you want to cancel a subscription from Apple - Apple Support

Do you have access to your mail box from another device?