afaik they are no longer available - try here
dial 150 or 0345 454 1111 and follow the prompts to - 'thinking of leaving us' - then "technical issues" - dont worry about that they do much more - open 8am -10pm 7 days a week - should take you to a UK call centre
the new thing is pods - https://www.virginmedia.com/shop/broadband/intelligent-wifi-pods-existing-customer
again afaik they are £5 a month - you can have up to 3 - no idea if that then becomes £15 - they are free if you are on the 1gig package or the top range package - again talk to retentions - i think the deal is you return the boosters and get the new pods to replace them
they only work with the hub3 and the hub4
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Tony