how to get a refund on incorrect bill in itunes

Ostensibly that looks like a legitimate notification. Did you perhaps install the app to test it?

Typically apps with free trials set up an auto-renewing subscription which you need to manually revoke before it is first called on if you don't want to continue with the subscription at the end of the trial. See View, change, or cancel your subscriptions - Apple Support for details on how to cancel any upcoming renewals. Removing an app or not using it are not sufficient to prevent scheduled charges.

In principle all completed sales are final, however you can potentially request a refund via https://reportaproblem.apple.com/ for a recent unexpected payment that was taken, particularly if you can argue that you haven't made any use of the service and were unaware that the subscription had been created.

Alternatively review recent purchases at https://reportaproblem.apple.com/ or check your purchase history in iTunes and view your subscriptions. If you are the organizer of a family share check for purchases by other members.

See also If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support and About payment card authorization holds from the App Store or iTunes Store - Apple Support.

If you cannot identify the payment then perhaps you are looking at a phishing email. See Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support.

If there really have been purchases that you didn't authorize, or you've entered your Apple ID credentials at a fake Apple portal, see If you think your Apple ID has been compromised - Apple Support, change your Apple ID password, and if possible turn on Two-factor authentication for Apple ID - Apple Support.

See also Use Screen Time to prevent purchasing on your iPhone, iPad, or iPod touch - Apple Support.

• If there is no evidence of a charge on either your iTunes or bank/credit card accounts this is likely to be a phishing exercise which you should ignore.
• If there is a charge shown under your iTunes store account and it relates to misuse of your Apple ID then you need to start a conversation with iTunes Store support to get it cancelled and refunded, change your password, and enable two-factor authentication if at all possible.
• If it isn't connected to your own Apple ID but funds have gone from your bank or credit card account that purport to be from iTunes then the account has been compromised and you need to deal directly with your financial institution.

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