If the wired connections are all fine and stable and not dropping (are they?), then it sounds like the SH2 may be on its last legs. If you call then they will just send a Hub3 replacement. Try calling in again but 08.00 is the best time to get through with short wait times.
Another solution I have always employed is to just use my SH2 in modem only mode and use my own better quality wireless equipment. You could consider that - even when you get the Hub3 as well, if that doesnt solve wifi issues.
If you dont get the swap by tomorrow morning just post back here
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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.