purchase a gift with store credit.

"I've put into the account, and now it can't be used?"

You can use it for purchasing content for yourself. You cannot use it for gifts.

"When did this change? "

I don't remember ever being able to buy gifts with a gift card.

"I would like my money back."

Not likely

RoamingGnome is correct; you've never been able to purchase gifts for others with iTunes Store credit. Why this is the case Apple has never explained but they're not unique in this restriction. Amazon has a similar restriction unless they've changed very recently. So there's clearly some good reason, though what that reason might be I can't guess.

As to getting your money back, if you have not made any purchases since you redeemed the card, you can contact the iTunes Store:

http://www.apple.com/emea/support/itunes/contact.html

and make a request for them to put the balance back on the iTunes card. You could then give that card to someone else. If you've used up part of the balance, then getting any of that money back will not be possible.

Regards.