What should I do if Apple denied my refund request?

If it was an in-app purchase that you did not get, you can see if they are restorable here:

If you can't find or use your in-app purchases - Apple Support

The developer cannot issue refunds, but they are perfectly capable of issuing you a Promo Code for an in-app purchase that they did not deliver after receiving the funds. Claiming that they have contacted Apple with no response on your behalf is likely just to appease you so they are not being blamed. There is no direct communication from Developers to Apple for dispute resolution, there is only assistance for developers for coding their apps. You can also report the app to Apple at the reportaproblem link that you used to request a refund or write a review for the app in the App Store.

After contacting Apple and also requesting a refund, then the decision has been made by Apple and you will need to follow up with your bank for disputing the charge, contact your local regulators, or however you wish to proceed. I have seen where the payment method will no longer be valid after disputing a charge, but not your account being suspended. That is just my experience on what I have seen on this Support Site.

Please note that this Support Forum is not for Apple interactions and we are just users like you that have no influence and do not represent Apple's opinion or stance on any issue.

Speak to Apple Support.

Direct link to Apple Support options -

https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0245&symptom_id=23362

World-wide Apple Support -

Contact Apple Support - Apple Support

M1 Mac mini, macOS 15.3.1;  Watch, series 10 GPS-only, watchOS 11.3.1; iPhone 16, iOS 18.3.1; TV 4th Gen, tvOS 18.3; HomePods, audioOS 18.3 and Airport Express w/ Airplay 2

I have seen where the payment method will no longer be valid after disputing a charge, but not your account being suspended.

If a bank reverses a charge, the user will be in a default situation regarding a purchase. Apple suspends accounts when the user defaults on a payment.

BTW, I reported the previous comment, and it has been removed.