I can't say I'm surprised by what you report, but there is a way forward.
As you're in a fixed term contract and VM's customer service are useless, you'll probably have to use the VM complaints process (and almost certainly escalate for arbitration at CISAS ) to be released from contract without penalty. If you need to do this, the grounds of your complaint is the poor performance, and your request for release from contract without penalty is twofold: First the Consumer Rights Act 2015 that requires any consumer service to be provided with "reasonable skill and care" which in this context means a reliable connection and competent customer service, and second, the Ofcom Fairness Commitments, that state amongst other provisions "Customers’ services work as promised, reliably over time. If things go wrong providers give a prompt response to fix problems and take appropriate action to help their customers, which may include providing compensation where relevant. If providers can’t fix problems with core services they have promised to deliver within a reasonable period, customers can walk away from their contract with no penalty." Use the online complaints form buried in Virgin Media, ask for compensation for the lies that the problem had been fixed (a mis-selling matter) plus the subsequent poor customer service, as well as release from contract without penalty. This complaint WILL BE FOBBED OFF, I know this from personal experience at the moment trying to get the company to address a similar reliability complaint, and it is evident that VM are using slaves to issue meaningless drop-down box responses where the staff don't bother to understand or own the complaint, and offer "resolutions" that don't fix the subject of the customer complaint. I suppose you might get lucky and find they treat your complaint promptly, fairly and competently, there's a first time for everything. As far as my suggestion here is concerned, the reason for making the formal complaint is because you have to formally give the company the chance to deal with a complaint before you unleash the hounds. And you do that by rejecting the "resolution" that VM offer and asking for a deadlock letter, and when you get that, you immediately take the matter to CISAS, the industry complaints adjudication scheme - free for you to use, costs of several hundred quid always paid by the company.
The forum staff can try and help by giving things a prod here, and if that gets all of the outcomes you want then it would be quicker and easier than the formal route. Separately from your complaint, I'd also report VM to local trading standards - if this is a long standing fault, and they're continuing to rake money off customers and sell new contracts whilst throwing their hands up and saying "no idea what's wrong, never mind, not our problem", then they deserve to be taken to task.