Why was my app subscription refund request denied from the App Store?

Last week, I canceled an app subscription several days before its auto-renewal. Over the weekend, I received a charge for the app's next billing cycle. I checked my subscriptions and verified the status was indeed "canceled." I submitted a refund request, but got a response that my claim and purchase did not meet conditions for a refund. No further details. I have read the refund conditions and cannot find a reason for why my claim/purchase is ineligible. Can anyone point me in the right direction? It seems unjust to be charged for a service I canceled in advance and am no longer using. Is this a frequent problem with Apple? A scam?

[Re-Titled by Moderator]