Using iTunes CREDITS once I redeem my gift card

I cannot get iTunes to use my existing credit of $26.22. The last album I purchased went through my (stored) credit card instead of using the money I have available in credit. I'm talking about CREDIT that is stored in my iTunes app, already redeemed from a gift card. (Please see my screenshot.)

This used to be simple. Now there is no indication anywhere of how to do this. Not in the iTunes Help, and not in the iTunes forums. I'd appreciate any help anyone can offer.

Thanks!