Were you able to see if the charge is managed by Apple and showing in your Purchase History or as a Subscription?
View your purchase history for the App Store and other Apple media services - Apple Support
If you want to cancel a subscription from Apple - Apple Support
If you do see it there, then of course cancel the subscription first, then request a refund. It is true that you cannot request a refund for a Pending charge and will need to wait for it to be finalized, and in some cases Pending charges will just disappear and no further action will be needed.
Request a refund for apps or content that you bought from Apple - Apple Support
If you do not see that the charge is managed by Apple in those links, then it is coming from a third party or website and your bank (credit card company) does require you to make every effort to contact the merchant. If you are unable to find this person, then follow up with your bank (credit card) to formally dispute the charge. If the Credit Card company fails to honor your request to dispute the charge, then you need to contact your local government resources for consumer complaints. In the US, we have the CFPB to file complaints against Banks/Credit Card companies, and in most cases you get a response in 15 days.
The EU has further puts its consumers at risk by allowing apps to be purchased outside of the App Store. This bypasses Apple's ability to manage the purchase and puts the burden on the consumer to track down the developer. Apple does provide a couple support articles to help you find out where it came from, but has no ability to force them to cancel/refund your subscription.
About purchases not billed through the App Store or the App Store’s In-App Purchase system - Apple Support
Find out where you downloaded an iPhone or iPad app from in the European Union - Apple Support
