[Raistlin]

There are other examples on the forum here of people who have been mistakenly billed for premium rate calls that they didn't make, if you do search for 'premium' you should be able to find some of them.

I would suggest that you need to immediately contest the calls and get Virgin to put a bar on all premium calls from that line. Some people have had this done in the past, but premium calls have still been made on the line somehow - this seems to have been proof that there's an error somewhere in Virgin's system.