I read about 15 web search results about this, including many from community specialists. None of them really answered the actual question asked and just talked about how to get a refund. The best I could do was your credit note essentially acts as account balance and should be automatically used when you next make a purchase that you can pay for with account balance.
You may receive a credit note if Apple tries to refund a credit card payment but the card isn't working for them.
If you still have questions or problems:
To contact Apple, click here --> Choose your country or region - Official Apple Support
Select your country (also look for "other" regions), then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service by telephone --> Contact Apple for support and service - Apple Support
If you find out a definitive answer as to why it isn't showing in yur balance and if you have ot do something special to use it, please post the answer here!