If you are a Media customer with a VM landline you can contact them free on 150. Otherwise it's 0345 454 1111 or 0345 6000 789 (standard rate call) and ask to "opt out" of Virgin Media/Mobile marketing.
Once done it will take time for your preference to filter through all Virgin's systems but there will be a decrease in unsolicited contact.
If you want to say thanks > click 'Kudos'. Answered your question? > click 'Mark as Helpful Answer' also.