Are you experiencing a 'total loss of service' (TLS = no connection at all) or a slow down in speeds or an intermittent connection? Various options may apply depending on the exact problem.
A TLS should attract compensation under the auto comp scheme
https://www.virginmedia.com/help/billing-and-payments/automatic-compensation
although topics on here regularly describe VM trying to dodge paying what might be due.
What actions have you/VM taken to try to remedy the problem?
VM has signed up to the OFCOM fairness commitments
https://www.ofcom.org.uk/phones-and-broadband/access-to-decent-broadband/fairness-commitments
Under item 4 you should be able to leave without penalty if VM cannot resolve.
Have you made a formal complaint to VM about the issue?
https://www.virginmedia.com/help/complaints
That would be a required first step but, in all likelihood, it will not result in a useful outcome.
From there you could go to arbitration via the timescales and processes below
https://www.commsombudsman.org/our-process