Are connections on ethernet cabled devices ok? If so and the problem is wifi only then boosters are not a good option. The maths says that you would be better advised getting your own better quality wireless equipment to solve the wifi connection issues once and for all. It will be your yours to own forever and to take with you if you move supplier.
Oh - and whatever you do - dont cancel the DD - VM will just mark your credit file as a "defaulted payer" and that's a nightmare to get removed.
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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 +2 Airport Express's. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.