Android 8. 0 problem found, which can result in unforeseen expenses. The smartphone consumes mobile traffic even if it is connected to a Wi-Fi point. Google is not yet ready to solve this problem, but there are workarounds.

The first way. Completely disable the use of the Internet over a cellular network. In this case, the smartphone will connect to the network only through Wi-Fi, without resorting to traffic, which provides a mobile operator.

The second way. Enable settings for developers and disable them in the option of continuous use of cellular data.

Apparently, Google namudrila with the settings for developers and included the necessary option for some of them to all users. Probably, in the near future Google will release a patch that fixes this problem.