Apple is not a bank or credit card processor. Apple is not a part of the return process. When a merchant accepts a return and processes a refund request, the merchant’s credit card processor debits funds from the merchant’s bank account and transfers the funds directly to your bank.
I suspect the merchant is still holding the request and not finalizing the transaction (refund). Please contact the merchant and request the Acquirer Reference Number (ARN). Provide the ARN to your bank and request they trace the refund.