If it's a newer box (V6, 360 or Stream box) then you will be charged if you don't return it.
You can print out the label I advised in my previous reply and use that to return the kit via yodel. It doesn't have to be the original packaging, just ensure the packaging is strong. Make sure you enclose a covering letter with it including serial number of the equipment, your account number and address, and obtain a tracking number from yodel so you (and VM) can keep an eye on it's progress.
Again as per my previous reply you can also return the equipment to an O2 store, and again, obtain a receipt and ensure you enclose a covering letter with it including serial number of the equipment, your account number and address.
You can also order prepaid packaging from https://www.virginmedia.com/help/virgin-media-return-or-recycle-equipment/request-returns-pack
The charges for non returned returned equipment are copy pasted below (taken from the Non Returned Equipment section at the bottom of the https://www.virginmedia.com/legal/price-guides page
- Hub 3: up to £50 per unit
- Hub 4: up to £75 per unit
- Hub 5: up to £75 per unit
- Hub 5X: up to £85 per unit
- Emergency Back-up Line: up to £50 per unit
- Wired Booster: up to £50 per unit
- WiFi Booster: up to £50 per unit Intelligent
- WiFi Pod: up to £86 per unit
- Virgin TV 360 box: Up to £100 per unit
- Stream box: Up to £45 per unit
- V6 box: up to £100 per unit