Got receipt for an unauthorized purchase, please help!

Let's be clear, the only iDevice we own is a single iPHone 3GS:

Last night I received an invoice stating I downloaded a free App called Texas Poker from KAMAGAMES LTD. The app, which I have never downloaded (it isn't in my iTunes nor on my phone), has made two in-app purchases:

Texas Poker, 500k chips, Seller: KAMAGAMES LTD 9.99

Texas Poker, 500k chips, Seller: KAMAGAMES LTD 9.99

After taxes, this total invoice comes out to 22.76$, which is the total amount I had left in my account from a gift card I had redeemed a couple of months earlier.

I have never downloaded such an app, therefore these in-app purchases are impossible for me to have made. I reported this by e-mail to iTunes support but it's the weekend and I really want this settled ASAP.

Thank god I did not have a credit card linked to my account.

What can I do from this point on?

All of this follows my installing of an app called Paperboy:Special Delivery, which is free and does not allow for in-app purchases.

I do not gamble and NEVER play poker.

How can I get my money back from this illegal, unauthorized purchase?