A repeat instance of this. Virgin Media should be ashamed but won't be because they don't care.
Staff here can probably get this sorted, including the compensation you're due for (a) the poor service in trying to close the account and for continuing to bill for services not required, (b) for not sorting it out and lying about fixing things when contacted, for (c) blackmarking your credit history, and for (d) passing the debt on to the scummy debt collection agency. By my reckoning that's four CISAS Tier 3 failure (deserving compensation of say £150 each), wouldn't you agree forum staff? Here's the way I've concluded that. A spoiled credit history lingers for six years, and will affect new credit agreements, credit card applications, future phone contracts, new mortgages or rental contracts, or even come up in pre-employment checks. In addition to the settlement figures above, the resolution needs to include that the company correct your credit history.
If you've already raised a formal complaint and been fobbed off, then you can ask for a deadlock letter and then take the matter to CISAS, the industry complaints adjudicator. If you haven't got a formal complaint then you need to do that and get a deadlock letter before approaching CISAS. It will be quicker and easier for you if forum staff can intervene and bypass the imbeciles of customer services and the equally useless complaints team, but they can't get involved once a matter is sent to CISAS, so maybe give them a couple of days to come up with an offer of settlement that covers all the points above, and is suitably generous. Since VM will be charged case fees of about £400 is CISAS get involved, you shouldn't settle for less than you think is entirely reasonable. If it goes to CISAS, data shows the vast majority of cases are found in the customer's favour, or VM immediately concede.
And finally, complain to Ofcom, and do it today. They won't get involved in your complaint, but they monitor VM's performance on complaints and service standards, and by complaining you're helping add to the evidence that will hopefully result in a proper regulatory investigation. I'd suggest you comment in the Ofcom complaint that this fiasco around the supposedly simple business of closing an account is a particularly serious breach of Ofcom General Condition C1.8, which requires that cancelling a contract is quick, simple and easy.