Yes, this happened to me recently and was the result of some kind of fraud on my account, somebody had somehow gained access to it and used my account to purchase apps, and I didn't find out until I received the receipt from Apple.
If you search for "hacked", "fraud", etc. on this forum, you will find other such reports. And doing a similar search for "iTunes Store fraud" on the web will turn up a lot of recent stories connected to this issue. So, you are not alone.
Immediate security procedures you should now follow:
1. Change your iTunes Store password to something difficult to guess (mixture of letters, numbers and symbols).
2. Change your secret question and answer.
3. Remove your payment details from your iTunes Store account (choose the "none" option).
4. With your bank, cancel your credit or debit card used to make iTunes Store purchases. Notify your bank that you have been charged for items you did not purchase and that you wish to dispute such charges / register this as fraud / claim the charges back. The bank should then take up this matter with Apple on your behalf.
Based on my own experience, trying to contact Apple yourself about any of this is pretty much pointless, they don't have phone support for the iTunes Store, you have to send them e-mails, which then go unanswered or which eventually come back with computer-generated generic responses, often not relevant to your specific issue at all. The only reason really to contact Apple is if you want them to disable your account.
Good luck!
