All TV boxes older than the Tivo are obsolete and do not need to be returned to VM, they will tell you to take them to your local council recycling centre.
If VM have not requested the return of the Tivo box and sent return packaging then it may also be too old for them to reuse, but you need to call VM and check or wait for the forum staff to get to this thread and they should be able to check your account and confirm if they want it back or not.
Disclaimer - I don't work for Virgin Media. I'm just another VM user trying to help out. My setup: V6 TV box, Vivid 200 Optical fibre with Hub 3 in modem mode connected to a Netgear R7000 router. Telewest/VM user since 2001.