Hi BobT,
If you briefly explain what the problem is with your faulty tivo box, along with any onscreen error messages and codes the forum team may be able help remedy the box issue(s) from here. They may also be able to help with registering for POA.
Details and a contact email address to register for POA are available on the following page
https://www.virginmedia.com/help/accessibility
The info below is a copy paste from the Extra support & services > Power of Attorney and other court appointed third party account management sub section from the above linked page (the copy paste doesn't include the contact email address as the forum software removes it)
"If you need to tell us that you have given power of attorney to a friend or family member, or if you are the friend or family member of someone who has been given power of attorney, you can let us know by sending the confirmation or certified copy of the confirmation to us detailing the specifics of the change.
The address to write to is;
Virgin Media
Sunderland
SR43 4AA
We recommend that you send us these documents to us using a recorded delivery. We will return the documents to you once we have received them and we’ll send a confirmation letter to you within 48 hours, though it may take a few days to arrive."