Another way you can be charged for a supposedly "free" call is if you use the 1471 service to get the number of a missed call and then take the option to dial 3 to return the call. In that case you not dialing the number direct but via a third party.
Coenoby
******************************* I am just another Virgin Media customer. If someone posts a useful reply you can say thanks by clicking on the thumbs up sign in their post. If someone posts a message that solves your problem it helps everyone if you mark their post as a Helpful Answer
I'm not able to locate any account details for you, are you able to pop me over a private message including your address details and I'll be able to take a closer look.