Hi, and welcome to the Apple (user-to-user) Community!
Re: How can I cancel a subscription on an old Apple ID?
Sign in with that old Apple ID and use the steps in this article to cancel the subscription.
See what to do: If you want to cancel a subscription from Apple - Apple Support
or
Cancelling subscriptions is slightly different in Germany, Israel, South Africa, and Turkey
See: About canceling subscriptions in Germany, Israel, South Africa, or Türkiye - Apple Support
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Re: old Apple ID account: I need to access it so I can stop the charges
If you find you need to recover the old Apple ID Account:
You may want to learn about using account recovery .
How to use account recovery when you can’t reset your Apple ID password - Apple Support
or
If needed:
You may want to reach out to the Billing and Subscriptions Support Team. They have a "Get Support" link (online chat / phone / email etc.) at the bottom of their webpage (link below):
Subscriptions and Billing - Official Apple Support
All the best :-)