There are many methods for cancelling subscriptions and you can check those options here. It can even be done from an Android device.
If you want to cancel a subscription from Apple - Apple Support
If you are still not able to use one of those options, then you can contact Apple directly here:
Contact Apple Support - Apple Support
Cancelling a subscription does not erase any previous charge that you owe. That is an agreement to pay the subscription price until you cancel the subscription yourself. Not using the subscription will not cancel it or prevent a charge.
You can delete your Apple Account be following the link here. You will want to resolve the subscription charge first and also review all details about account deletion. If you happen to have that account logged into any device when you delete it, the device will be locked to the account and you will no longer have a password to remove it.
How to delete your Apple Account - Apple Support