Even if the number is correct, I still think it's number spoofing by a scammers or scammers operating separately but from the same call centre, or something along those lines. It would explain why having a current contract or being opted into marketing seems irrelevant.
Funnily enough, the only time I've ever been scammed genuinely was Virgin. They had contracted out to a third party, no doubt the cheapest available, who were using dodgy tactics to trick people into signing without knowing the full details. The tactics weren't approved by Virgin, of course, and I believe the contractors were caught and punished, but the point is that it can happen, and no doubt more so when monkeys for peanuts is your ideal employee.
Virgin/Sky/BT/Apple/Windows/HSBC/Barclays/Natwest/Amazon... these companies are common target brands because the companies are so prevalent. You don't have to know who is a customer, chances are good you can just guess and be right. If you're wrong, just hang up and ask the next random person about their Virgin account. Knowing your name is a useful bonus but not necessarily required.
I'm mildly amused by the official responses to customer services sounding like scammers. Just "oh yeah, that's us".
