I think you need to secure it. Some routers here share with other than your own. That is this.
http://www.extremetech.com/computing/184263-comcast-turns-50000-paying-customer-homes-into-public-hotspots-millions-more-by-the-end-of-the-year
As I don't know BT, you must control your hotspot. It sounds like you don't.
So here's the deal, I live in a shared house with shared access to the router.
Since moving in I've had trouble with various things like access control and firewall settings being applied to my Xbox one and messed around with on the router management console. It's a BT home hub 5. I've had to reset the password many times to then remove restrictions, plus reset to factory settings multiple times. Whoever is doing it, is putting their device on the DMZ option within the router. Perhaps hosting a server. My knowledge of what is happening is growing as the attacks and restrictions evolve. Most recently being the blocking of the Xbox ones ports, and now, today my multiplayer connection speed is down to 4 Mbps, usually 30ish, I just know that someone has restricted it and I have no idea how. Here's a link for screenshots of event log, any educated 'light shedding' would be greatly appreciated. http://imgur.com/a/QokIS

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