You wouldn’t be double billed for the same subscription on the same account. That’s not possible.
You might get double billed if two separate accounts signed up for a service, but with the same payment method.
You might get billed twice, for two separate services.
Fond out what the charges were for.
If you see 'apple.com/bill' on your billing statement - Apple Support
See your purchase history for the App Store, iTunes Store, and more - Apple Support
See your subscriptions overview - Apple
If you have multiple accounts that could be involved, then check for each.
You can cancel subscriptions that you do not wish to continue. How to cancel a subscription from Apple - Apple Support
Contact Apple for support and service (phone numbers) or start your support request online (chat/email/callback).