Virgin Media has changed it's opt-out scheme. Instead of sending them an e-mail you should now go to https://keepup.virginmedia.com/optout and fill out a simple opt-out form.
I've asked Virgin whether or not opting out will also stop mailings addressed to a generic addressee, such as 'The Householder'. I've not yet had a response but I'm assuming this is the case.
Please note that opting out will not stop unaddressed junk mail from Virgin. To stop unaddressed Virgin Media junk mail you need to register with Royal Mail's opt-out scheme for unaddressed mail: the infamous Door-to-Door Opt-Out. Signing up should stop unaddressed from other notorious junk mailers as well, including Domino's Pizza, Farmfoods, Talk Talk and Sky.