As far as I know it is absolutely impossible to have a duplicate subscription. You may be confused into thinking so if you use multiple Apple IDs or you are family sharing organizer. The support article If you see 'apple.com/bill' on your billing statement - Apple Support explains how you can check your iTunes and App Stores purchase history, cancel subscriptions, and track possible sources of unrecognized Apple charges you may see on a bill.
This support article explains how to cancel a subscription from Apple on an Apple mobile device, Mac, PC, and online ➔ If you want to cancel a subscription from Apple - Apple Support , or this video will only tell you how to do it on an iPhone ➔ https://www.youtube.com/watch/XXx-J-ueCtE
Notes:
• You might need to scroll down to find the Cancel Subscription button.
• If you don’t see Cancel Subscription, then the subscription is already canceled and won't renew. An "Expires" date (instead of "Renews") means the current subscription will just run until then. "Resubscribe" is just in case you change your mind about having it end.
• Deleting an app does not cancel a subscription.
• If you don’t cancel trials more than 24 hours before your renewal date, your subscription might renew.
• If you don't have an Apple device, see the options near the bottom of the support document.
• Many subscriptions are set to renew automatically until you intentionally cancel them.
If you can’t find the subscription that you want to cancel, use this shortcut to jump to the section about what to do. --> If you want to cancel a subscription from Apple - Apple Support If you still can't find a subscription, contact Apple Support using this issue-specific link at the end of the section. --> https://getsupport.apple.com/?caller=kbase&PGF=PGF63006&category_id=SC0060&symptom_id=23208
If you still have problems, contact Apple online using this page ➔ Choose your country or region - Official Apple Support Select your country, then a product. Alternatively, see a list of Apple phone numbers around the world ➔ Contact Apple for support and service - Apple Support