Why aren't iCloud and Apple Music fees deducted from my iTunes gift card balance?
My iTunes gift card balance is well over my iCloud and Apple Music balance, but the fees are still being drawn from my other payment method.
The fees for Apple Muic should come out of your iTunes credit balance. Read this Apple Knowledge base article on how to check your balance:
See your iTunes credit balance - Apple Support
If you have a credit balance showing then perhaps a call to Apple Support is in order... So read this....