Hello Hugoebostock
Thanks for taking the time to post in regards to your Virgin Media services and the Volt benefits not being applied, we appreciate you raising this via the forums and welcome to the community.
Although you don't need to be named on both accounts, both accounts do need to be registered at the same address for the benefits to be applied, it seems this is the case if O2 have already applied these to your mobile services.
When you sign into your O2 online account, does it advise that the Volt benefits are active or give you the option to activate them?
Rob