You may not realise this, but various apps are leeching on your mobile internet connection, resulting in greater data and battery use.
Android has a built-in tool to prevent you from exceeding your network limit, and if you’re not using it already, you really should be. Open Settings>Data usage to get started, and tap the switch to enable monitoring for mobile data.
Next, enable Set mobile data limit, and use the sliders to set a warning notification and upper limit. With this feature enabled, Android will prevent any data from being used once the limit is reached. But rather than reach this point, you can scroll down and put the brakes on the apps that have heavy data use. Simply tap the app you wish to limit and enable the Restrict app background data option.