For what it's worth, based on this community forum but also on various threads on sites like hotukdeals, I reckon Virgin Media operate a six stage approach to contract renegotiation.
The base stage is the working assumption by VM that most customers, as with bank and utility switching, don't have the time and energy to take the big companies on in a Moroccan market style haggle. It's just not British.
Those that do are initially tested by Stage One. This is bot land, be it online or via the phone, where you are offered a piffling fixed discount of, say, £3.50 for six months and is automatically processed if you assent. It saves both sides time and money and is a clever and probably effective rouse.
If you are bot-proof then you reach Stage Two. This will be, after a long queue listening to the same five annoying but deliberately upbeat songs, a nervous offshore level 1 fully scripted customer service rep with marginal discretion to offer a couple of quid more off than the bot.
If you say no (nicely) they will sound hurt and depressed and transfer you to a fully scripted offshore level 2 customer service rep with a bit more wriggle room (Stage Three) .
If you persevere you might then make it to offscript onshore retentions (Stage Four) who might even process a cancellation without hanging up on you.
If you have assented to receive VM marketing spam then you might get to Stage Five which is onshore unscripted level 1 outbound retentions with a tasty offer.
If you are really hardcore and still hold out then you might (possibly depending on whether you have a profitable quad play Oomph package) reach the onshore unscripted level 2 outbound retentions folk at Stage Six who offer you an outrageous deal that you would feel like a complete idiot to say no to.
Or you could just do yourself a favour and switch to good quality British companies who are straightforward and honest with you.