@Alenaradzevich Sometimes apps will run in background even you have not turned on data. Here the advice from moderator:
In order for you to have more control over you data usage, we recommend turning off data when is not needed. Also disabling Wi-Fi assist (for iPhone) or Smart network switch (for Android) to avoid the phone connects and jumps automatically from Wi-Fi to data.
It is also recommended to restrict background data to avoid that applications connect automatically to your data and make small updates as soon as you turn it on.
You may consider monitoring your data from the setting of your phone if you have an android (settings-data- set data limit – enter your billing cycle- your data allotment so the phones gives you a breakdown per app) .
You may also consider getting a third party application that will give you a breakdown of the usage per app, so you know what application is using your data or if it is the operating system of your phone.
