Go to Settings > System management/System > Backup & reset/Reset options, reset network settings, and then try again. * Note: Resetting network settings will reset your Wi-Fi, mobile network, and Bluetooth connections.
For Funtouch OS 9.0 and higher version, go to Settings>(Dual SIM cards and )Mobile network>Data monitor), then you can restrict the apps to use data in the background. For the below Funtouch OS 9.0 version, go to Settings>(Dual SIM cards and )Mobile network, scroll down, and then you will find Data-saving mode.