Is 0800 052 0800 a real virgin contact number as I've had two letters demanding money for a outstanding bill from a acount that was closed 4 & 1/2 years ago one from a solicitors and one from virgin. The solicitors letter is asking for a bank transfer into a acount they have gave sort codes etc
That number is listed as Virgin Medias Business broadband contact so seems legit...
I suppose the question you should ask yourself is "Do I owe them money?"
Not being funny, its just you could well have closed an account down and paid up to date, and theres an error on their part. But if you kind of remember "yeah there WAS something outstanding when I cancelled" its likely better you engage with them and sort it out.