Stuff is regularly tidied up by the Mods. See https://community.virginmedia.com/t5/Managing-Your-Account-Cable/Cancellation-Payments-Rip-Off/m-p/5605741#M274930

I suspect they have a whole department to do nothing but dream up ways of making cancellation as difficult as possible, including things like this to punish those of us who do cancel.  Sending any refund by cheque rather than direct debit is just another means of punishment, as well as a way of them keeping hold of our money for longer.  There's no reason they can't refund by direct debit, plenty of other organisations do it.  Perhaps they hope that cheques will go missing and not be cashed, and people will get so frustrated that they won't chase up on it.

Like you, I've cancelled because I'm due to move to an area where VM don't offer service.  I've been with VM since long before it was Virgin Media - I can't remember just how long but our original email addresses were @virgin.net.  But they clearly don't give a stuff about my previous loyalty or the fact I don't even have the option to stay with VM.  I've been content enough with the service to stay with VM all these years but after this experience with cancellation I'd never consider signing up with them again if it became an option.

I did manage to raise a complaint about overpayment and billing issues but I did it from my account before disconnection. 

But be warned, the emails I received were increasingly incomprehensible, possibly from people whose first language isn't English and who didn't know how to use Google Translate.  Or possibly from someone's toddler simply hitting the keys on a keyboard.  I asked very simple questions in plain English but never got any understandable response, just nonsense replies.  Much as it goes against my principles, I eventually gave up because it was like repeatedly banging my head against a wall.  

I started my cancellation process at the beginning of November 2024 so I'm now into the 3rd month.  It should have been simple, there was nothing complicated, I just said I wanted to cancel when my current deal ended.  But VM really go out of their way to make it as difficult and lengthy a process as possible, plus they keep your money long after they're no longer providing service and then charge for equipment that hasn't been returned because of their own delays.

I had to give up on the 'complaints' process for my own sanity.  But when I eventually rid of VM altogether I will add my case to the many others already registered with OFCOM for investigation.