@ellenAnne if you have a third party WiFi extender that could explain the issue. However even if you havent it is unlikely your neighbour has logged onto your WiFi unless someone has given them your WiFi password. If that is possible then chage yhecpassword pronto.
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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
