You may have enabled Wi-Fi+ so that your phone switches to mobile data if the Wi-Fi network lags.
If you have enabled Wi-Fi+, your phone will simultaneously connect to both Wi-Fi and mobile networks, and switch to the one with better stability. If your phone detects that the Wi-Fi network stutters, it will switch to the mobile network, so that your phone still consumes mobile data even if it is connected to the Wi-Fi network.
To disable Wi-Fi+, go to Settings, search for and access Wi-Fi+, and disable it.
Some third-party apps are designed to consume mobile data even with Wi-Fi connected.
Some third-party apps, such as online banking apps, may still consume mobile data even if they are connected to a Wi-Fi network. This issue occurs on all Android phones and cannot be resolved by changing the settings on your phone.
Such apps usually do not consume much mobile data. If your phone has connected to a Wi-Fi network, you can disable Mobile data by performing the following: Swipe down from the status bar on the top to show the shortcuts menu, and disable Mobile data.
