@Cumbers many phones revert to mobile data when that is faster than a wifi connection. You can change this behavior by going into the phones set up for mobile data and turning off options called something like Wifi assist.
Taken with your other issue it sounds like poor wifi coverage in your home. You can help by making sure your Sky hub is as high innthe room as you can get it and not having the wifi signal blocked by furniture or radiators. However in many homes the free wifi router Sky provides is never going to give gast wifi innevery room which is why therecis a marketvfir third party wifi kit.
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65inch Sky Glass, 3 Sky Streaming Pucks, Sky Ultrafast + and Sky SR213(white Wifi Max hub) main Wifi from 3 TP-Link Deco M4 units in access point mode
