I was charged 9.99

See Avoid phishing emails, fake 'virus' alerts, phony support calls, and other scams - Apple Support in case you are responding to a fake alert.

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.

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