Cancel subscription.

If it doesn't appear in your Subscriptions maybe it's because you did not subscribe. Were you notified by email?

In a message Apple will always address you by your real name, never by your email address or Dear Customer. Also the sent-from address should be @apple.com or @itunes.com Additionally Apple does not send attachments.

Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support

Forward it as an attachment to reportphishing@apple.com

That's not in the regular subscriptions page because it's an iCloud service, not something purchased through the iTunes or app store.

See this article: https://support.apple.com/en-us/HT207594