I never signed up for this service
I never signed up for iTunes account Apple TV how do I Find out who did it and cancel
iPhone SE, iOS 14
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Cancel your subscription
This Apple support Billing Article should answer your question.
Subscriptions and Billing - Official Apple Support
then Make sure you have another method of receiving auth codes like another trusted friend’s mobile
https://support.apple.com/en-us/HT204915
you need to log into icloud.com and make sure unknown devices are removed from your account.
https://support.apple.com/en-us/HT204074
More important
change your Apple ID password.