I had this myself a few years ago - first I was aware was when I received a paper invoice thanking me for my order. I remain to be convinced on Vodafone's explanation at the time (my online account wasn't hacked - this was done over the phone). The do apparently have the ability to apply "extra" security to your account which supposedly means you get asked additional verification questions over the phone, although its probably pointless when their own phone system presently won't correctly recognise numbers or peoples security PINs automatically.
..In fact come to think of it - this could well be something someone has taken advantage of - if their automated PIN entry isn't working they'll only ask basic security questions over the phone which are IMO easy to guess.
