First off - which boxes do you have? https://www.virginmedia.com/care/tv-fault/which-tv-box
TiVo & V6 both run TiVo software and multiroom boxes are fully-functional, each with their own hard drives.
TV360 runs Horizon software and is designed around one central "master" box with the hard drive & subsequent "mini"boxes without hard drives.
Thus if you are a TiVo/V6 customer you get a much better deal than TV360 users by having multiple master boxes and no such thing as a mini-box.
Some "Volt" packages include an additional multiroom box as standard, otherwise there's likely to be an extra monthly fee ~£10 or so for the extra facility, which includes replication of your existing TV package onto the new box. You'll need an additional co-ax connection in the location you want to use the extra box, and if you don't have this then a manned install will be required.
You will likely need to call in to arrange this. What's the issue you're having with the 150 IVR?