I was charged $90 for the annual subscription, but I don’t want it anymore. I previously bought this and used it for school, but didn’t realize it was renewed today. I don’t need it anymore.
Whatever you were subscribed to can’t be Anki. Anki is free (the only paid part is the iphone app, and even that is a one-time purchase, not a subscription).
I’d recommend you to check again, where your subscription has come from, and redirect the request accordingly. You might be confusing this with AnkiHub or one of many similar apps that might still have “Anki” in their name, for example.