@danx55: Your phone will only ever automatically connect to a Wi-Fi network if you have manually connected to it previously. To prevent automatic connections with pre-established networks, please head to Settings > Connections > Wi-Fi > Tap the cog symbol next to a Wi-Fi connection > Auto reconnect > Toggle this option off > Tap the Back button > Tap the 3 dots in the top right > Advanced > Turn on Wi-Fi automatically > Off.
