VM no longer supply boosters - its Pods from now on.
However I believe they still have some old stock of boosters that they can use to replace faulty ones. You can try calling it in as a fault and take your luck that the CS rep knows what you mean and can sort it - without trying to get you to rent a Pod for £5/month (unless you qualify for a "free" one).
TBH - I would replace them with my own or a basic Mesh system. Look at the TP-Link range of powerline adapters with wifi - and their Mesh sytems
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John
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I do not work for VM. My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired, 2 on WiFi) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's & TP-Link Archer C64 WAP. On Volt 350Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.