I recently signed up with Vodafone who have arrived in Cambridge and finally put an end to VM's monopoly. Slightly faster, less than half the price I was being charged - what's not to like?
Which only left me with the tricky issue of cancelling my VM contract. First I tried phoning like they ask, but of course got fed up with waiting. Especially ended up with the suspicion that once you select the 'I want to cancel' option they artificially lengthen the queue.
So I set myself the challenge of cancelling without phoning or struggling with the chat system. Pretty tricky since they go to such lengths to hinder any online contact. However there is a tiny gap in their defences, the complaints page at https://my.virginmedia.com/my-cases/make-a-complaint. So I duly raised a complaint about the phone waiting times, at the same time taking the opportunity to request cancellation. (I'd already taken the precaution of cancelling my direct debit.)
A mere couple of weeks later an email arrived from the 'Resolutions Team', saying that "we cannot process cancellation ... as we require a verbal confirmation from your end." To which I replied that they were being deliberately obstructive, but were free to call me themselves if they wished.
Then nothing, except that I continued to be billed. The most promising way to apply a bit of pressure looked like CISAS https://www.cedr.com/consumer/cisas, and this turned out to be the case in the end. However they won't even look at your complaint until it's at least eight weeks old.
To pass the time I tried ISPA https://www.ispa.org.uk/consumers/complaints which is VM's trade association. They have a very convincing system where you register a complaint, then escalate it in the event of no response from their member. The only trouble was, it had absolutely no effect.
Back to waiting until my eight weeks were up, at which point I received a nice email from VM's system telling me about CISAS (so all my previous research was unnecessary!).
Anyway to cut a long story short, I duly registered my complaint with CISAS. They demand lots of supporting documentation so I sent them my latest bill and screenshots of all the emails wrapped in a Word document.
And VM surrendered! Contract cancelled, outstanding bills credited, even an apology that seemed written by a human being.
So it can be done, you just have to wait out your eight weeks and be prepared to handle the CISAS process.