I've just had a call saying exactly the same thing; £750 worth of "Monthly Gift" transactions against my account. Luckily my bank was good enough to spot it and is in the process of refunding the charges, but it's still very frustrating! I'm also completely clueless as to how they got access to my account. I consider my password to be pretty secure (over 15 characters, including letters, numbers and symbols), so I can't imagine they brute forced it?!?
What I find really frustrating is the lack of phone support from Apple in the UK! Surely with their enormous user base we should get more than a sodding email support form?!?