Redeeming iTunes account balances

My iTunes account says I have a $10 balance (from a gift card) , but when I go to buy music, my debit card gets charged instead. I cannot find a way to buy using the account balance funds. I also see that there is no longer a "BUY" option next to music, but instead I see "GIFT THIS SONG" as an option. iTunes is getting harder and harder to use. Need help!