Different customers experience different procedures when leaving VM (this is VM after all!). Some get a notification/confirmation from VM, some get none.
You have the tracking receipt from your delivery so you have a third-party reference of when VM received your notice to cancel.
Shortly after you are disconnected you should receive a final bill. If you are in debit, you pay the balance and leave VM. If you are in credit VM should refund you (although not necessarily quickly).
Once you have been disconnected you should receive returns packaging from VM (although non-receipt of packaging is a regular source of complaint on here). You may need to request it.
https://www.virginmedia.com/help/return-or-recycle-equipment
VM doesn't routinely remove cabling or wall boxes from past installations or make good same.
One of the VM forum team may be able to confirm your disconnection date for you. They usually reply here within a few days.