iCloud subscription

Looks like scam / phishing.

Your iCloud plan can't just disappear. You are the only one who can downgrade your iCloud+ plan.

See the following Apple articles:

If you think your Apple ID has been compromised

If you think your Apple ID has been compromised - Apple Support

Recognize and avoid phishing messages, phony support calls, and other scams

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

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If you receive a suspicious email or SMS text message that looks like it's supposed to be from Apple, please email it to reportphishing@apple.com

How to report suspicious emails, messages, and calls

• If you receive a suspicious email that looks like it's supposed to be from Apple, please forward it to reportphishing@apple.com.1  
• To report a suspicious SMS text message that looks like it's supposed to be from Apple, take a screenshot of the message and email the screenshot to reportphishing@apple.com.
• To report spam or other suspicious emails that you receive in your iCloud.com, me.com, or mac.com Inbox, send them to abuse@icloud.com.
• To report spam or other suspicious messages that you receive through Messages, tap Report Junk under the message. You can also block unwanted messages and calls.
• Report scam phone calls to the Federal Trade Commission (U.S. only) at reportfraud.ftc.gov or to your local law enforcement agency.

After you reported, remove that message and see -> Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch -> Clear the history and cookies from Safari on your iPhone, iPad, or iPod touch - Apple Support

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Additional: to keep your Apple ID account secure, see the following Apple articles: 

See who has access to your device or accounts

See who has access to your iPhone or iPad – Apple Support (UK)

Delete suspicious content from your devices

Delete suspicious content from your devices – Apple Support (UK)

Check your Apple ID device list to see where you're signed in

Check your Apple ID device list to find where you're signed in - Apple Support

• if you see devices that don't belong to you, delete from your account.

Personal Safety User Guide -> Personal Safety User Guide – Apple Support (UK)

Manage and use your Apple ID -> Manage and use your Apple ID – Apple Support (UK)

(if you haven't already done this) Two-factor authentication for Apple ID -> Two-factor authentication for Apple ID - Apple Support

Change your Apple ID password -> Change your Apple ID password - Apple Support

• Create a strong password for your Apple ID, It is best if your password consists of eight or more characters and include upper and lowercase letters, and at least one number. You can also add extra characters and punctuation marks to make your password even stronger. 
• Never provide your password, passcode, security questions, verification codes, recovery key or any other account security details to anyone else. Apple will never ask you for this information.

Then see this Apple article: What to do after you change your Apple ID or password

What to do after you change your Apple ID or password - Apple Support

Never jailbroken your iPhone.