Apple support have an article online (link below) that may help:
Re: App Store
What to do: If you want to cancel a subscription from Apple – Apple Support
or
If the subscription that you want to cancel is not listed – Apple Support
Cancelling subscriptions is slightly different in some countries:
About cancelling subscriptions in Germany, Israel, South Africa or Turkey – Apple Support
If needed:
Try using the same app that charged you, or contact it's merchant, or website, to cancel.
How to contact an app developer: How to contact an app developer - Apple Support
How to: Contact a third-party vendor : Contact a third-party vendor - Apple Support
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Re: "It is a free subscription that automatically renews as a paid subscription"
Seems you need to cancel a free trial at least 24 hours before it expires, losing access to it immediately, yet escaping any future charges.
If Apple has the payment:
You may want to try requesting a refund, and wait to see what Apple decides:
(If a refund is granted the money returns to the payment method used, in time.)
If money has been deducted (not pending):
How to:
Request a refund for apps or content that you bought from Apple – Apple Support
All the best :-)