Like to give my notice

https://www.virginmedia.com/help/leaving/

and you may possibly also be able to use the other online options here

https://community.virginmedia.com/t5/Managing-Your-Account-Cable/renewal-deals/m-p/5587739#M271957

If you simply wish to cancel, with no further negotiation or discussion with VM …

You can cancel your services by post as per info below. You can send your leaving request by post to:

Virgin Media, Sunderland, SR43 4AA

Use a first-class, tracked delivery service. This will give you a date/time of delivery when you gave VM your 30 days’ notice to cancel. Also keep a record of the tracking number.

If your disconnection happens during a minimum term period VM may charge you early disconnection fees.

You can also share your unhappy cancellation experience with OFCOM.

They launched an investigation into VM on 13 July 2023 specifically into VM's cancellation and complaints processes.

https://www.ofcom.org.uk/about-ofcom/bulletins/enforcement-bulletin/open-cases/cw_01275

Case ref. no. and an email at the bottom of the above page or submit with same info via the contact form

https://ofcomforms.secure.force.com/formentry/SitesFormCCTMonitoring

Submitting information won't help your individual complaint but it will contribute to the OFCOM investigation and it sounds like your experience is directly relevant to the terms of reference of the investigation.