Getting charged on an old apple account that I can't log in to

You need to regain access to the account to cancel any associated subscriptions on it.

click here ➜ If you forgot your Apple Account password - Apple Support

or here ➜ How to use account recovery when you can’t reset your Apple Account password - Apple Support

Once you regain access to the account, follow the steps in the link below to cancel the subscription.

click here ➜ If you want to cancel a subscription from Apple - Apple Support

Usually the phone number is one that was used on an iPhone that was logged in with that Apple ID.

It should always be a phone number you know because it was linked to an iPhone you used that Apple ID with.

How to use account recovery when you can’t reset your Apple Account password - Apple Support

If you don’t know which email address or phone number you use with Apple Account, try different email addresses or phone numbers. You can sign in and reset your password with any email addresses or phone numbers on file in your Apple Account.

There is no other way to do this. Apple cannot access your account and cancel the subscription if you can't verify you own the account.

Outside of that, you would need to cancel the associated credit card so it can no longer be charged.

Possibly, but they may just redirect you to the website to recover your account.

https://getsupport.apple.com