Unfortunately when Virgin Media get it wrong, they properly mess things up. Most customers installs go smoothly but on the occasion when they don't it seems that there are no clear mechanisms in place to get a fast track solution.
Having said that problems like the underground duct being damaged, aren't going to be apparent until they try pulling new cable through and then things get complex when they need someone to start digging holes in the public pavement.
Rather than dawdling though the official complainst proceedure, you may find a faster response if you contact the ceo, whos office has the clout to get VM's people to actually speak to each other.
neil.berkett@virginmedia.co.uk