They are "bull*******" you - see the web site - below - clearly says "2 V6 boxes".
Try calling “Retentions” on 150 or 0345 454 1111 (or 0800 9528046) - options 1-1-4-5 "Thinking of leaving" - they are open Monday – Friday, 8am - 8pm and on Saturday from 8am - 6pm. – [08.01 is best!]) you have a better chance of getting a UK call centre (it could still be a 30’+ wait though) who will be more understanding and helpful - explain the situation and they will sort you

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Services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.