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
https://www.virginmedia.com/help/leaving/
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. I have found that RM signed-for services are a dead loss these days and rarely get a signature so use a service that tracks and confirms delivery.
Be aware though, giving notice to finish on the end date of your minimum term does not mean an instant end to dealings with VM in the sense that the final billing, return of equipment etc. only happens once you are disconnected. You also need to consider your billing periods and direct debit dates as part of the process. Usual advice is to leave the direct debit in place until you are certain all of your dealings with VM are concluded.