Showing "Return Completed" as status but didn't receive refund yet
It can take 5-7 days once the goods arrive back at the warehouse.

From the refund page:


  Once your goods are back at Apple’s warehouse, your refund will be processed. Please allow 5-7 days for the refund to reach your account. For cash payments such as cheque and wire transfer, we will require your bank details, including IBAN/SWIFT, to proceed with the refund to your account.


If you haven't received your refund contact Apple Support. I would give it  a bit of time since it is holiday time.