Do you have the external "Omnibox" fitted to you wall? If so, trace the cable coming out from it to where it enters your property. What is on the internal wall at that point? Sometimes its a loose cable, or its been covered/hidden behind decoration, or even removed by a previous occupant.
Post up photos if you find anything
If not you will need to call in for a Tech install - try on - 0800 052 1734
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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, 1 WiFi, 1 on PA) Hub5 in modem mode with Apple Airport Extreme Router +2 Airport Express's. On 250Mbps, Talk Anytime Phone, x2 Mobile SIM only iPhones.