I've had the same thing, 12 times i think this week. Spoke to them once (its a work phone so wan't to worried). They started to talk about deals, despite our only joining virgin in December. Wanted to confirm my address and at that point I pressed them on what the call was about before I give out any details. Pointed out the dodgy number and eventually they hung up on me
Very frustraiting though. Looks like there have been a few other posts on this formun and it seems like the calls might be legit, but in this day and age it I wouldn't trust it.
Far from making me feel warm and fuzzy about possible offers, it just makes me think so one is trying to get my personal details for dodgy reasons.
Weird number, dodgy sounding call centre, calling several times a day - even when you have told them to not phone. Not good!