You could try calling “Retentions” on 150 or 0345 454 1111 - options 1-1-4-4 "Thinking of leaving" - they are open 8am until 9pm but calling early between 08.00-09.00 am (midweek) is best, when you will usually get a UK call centre who’s staff are more informed and helpful - if you do get routed "offshore", just insist that you want to cancel and they will have to transfer you to that UK based department.
Tell them you are thinking of leaving for Sky/BT/whoever because of this issue - and they will try and sort it for you (as it’s their job to keep customers).
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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 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.