If you do in fact have 2 Apple Accounts, there is no way for Apple to know if they belong to the same person so no way to flag subscriptions on both as duplicated. You are entirely responsible for managing your accounts and any subscriptions you activate on each account. Apple will not do it for you.
You need to log in to the one of the accounts and cancel the subscription you don't want, then log in to https://reportaproblem.apple.com to find the charge and request a refund for it.
click here ➜ If you want to cancel a subscription from Apple - Apple Support
If you don't have another device that listens logged in to the second Apple Account then you can log in to https://account.apple.com and cancel it from there.
Once it's cancelled you can request a refund for it.
click here ➜ Request a refund for apps or content that you bought from Apple - Apple Support