Since around January I've been getting several phone-calls per month from individuals claiming to represent Virgin Media. They are very convincing, asking for me by name and engaging me in discussion about service enhancements (e.g. bandwidth upgrades, sport channels, new packages etc.
For the first few times engaged with the caller, explaining that I would prefer to keep what I've got or negotiate a reduction in price for a reduced service, but as they weren't authorised to offer anything like that I politely declined.
More recently, the callers have been calling from what appear to be mobile numbers, usually on poor quality phone lines, and I've taken to hanging up immediately they say who they're calling from. I wanted to make sure you're aware of this, and whether you agree with me that this sounds like some kind of scam operation, using Virgin Media's name to obtain my bank or card details.
There have been regular mentions about this on the forums. VM forum staff have confirmed in the past that some sales staff are working from home and some are using mobiles to make sales calls. IMO, however, your approach to be extremely wary of such calls is the right one.
It has also been mentioned on the forums in the past that some of these calls (where the caller knew a lot of information about the customer and their VM account) in fact turned out to be scams. Caller ID is also easily faked and cannot be trusted to identify the source of an in incoming call.
If you do not want to receive these sales calls, sign into 'My Virgin Media' and set your marketing preferences as appropriate. That way if you get future sales calls claiming to be from VM then they are likely to be fake. Also worth noting that VM do not make unsolicited outbound technical support calls so any calls of this kind are always scams.