In most cases all purchases in the App Store are final. At times Apple may provide a compassionate refund, but it should never be expected. It does appear Apple has given you a compassionate refund before, but that certainly does not mean you will get a refund every time.
You don't explain how this accidental purchase happened. It really is impossible to accidentally purchase something in the App Store because it requires you to double click the side button with the amount showing on the screen, followed by verification with FaceID/TouchID or Passcode. It is not like you can accidentally tap a button on the screen and be charged.
What is more likely is that you signed up for a free trial where you would see the:
- Trial period
- Subscription Start Date
- Subscription Price
- Subscription Length
- Message stating to avoid charges you must cancel a day before the subscription starts.
It may have been the case that you forgot to cancel the free trial and if that is the accident you made, then I would recommend to set a reminder to cancel if it is something you will not remember. It is as easy as saying "Siri, remind me to review my free trial in xx days". If that is the same reason you got a refund before and you have done nothing to prevent it from happening again, then it is understandable that you will not continue to get refunds.
When you request a refund and it is denied, you usually get 1 appeal. If that is denied as well, then the decision is final. There is not an explanation, it is either approved or denied. Make sure you cancel the subscription by following the steps here. This will prevent the subscription from being renewed next year.
View or cancel app subscriptions on iPhone - Apple Support
