The terms and conditions for using subscriptions through Apple, using the App Store, or using in-app purchases, say that all sales are final. Exceptions can be granted by the Apple staff on a case-by-case bases. The decision is theirs alone. Refund requests should be asked as soon as possible, before Apple has paid the developer/app publisher, which happens in monthly chunks, a few weeks after the transaction. The reason or motivation will be considered.
I was previously paying for a monthly subscription then all the sudden it changed to a yearly subscription
The user must have authorized that, although some may have used tactics that didn’t make the consequences very obvious. Always read the fine print and terms and conditions. Tapping “OK” may be enough for your agreement to a change.
… for a subscription i do not even use.
You pay subscription fees for access to the subscription content. Whether you use it or not, plays no role whatsoever. Be sure to cancel any subscription that you do not wish to continue. You may want to review that regularly, if you find that you have subscriptions “unknowingly”.
Each subscription requires user authorization (password, passcode, passkey, or Face ID/Touch ID). Misunderstandings often come from “trying out”, which already may start a subscription with free or discounted trial, that will auto-renew at regular price after that trial period. Deleting an app does not end the linked subscription; those are independent of each other.