To see your current data consumption for mobile you can check your Clientzone account, like you would check your DSL data.
As for monitoring bandwidth it becomes a bit tricky. There are multiple apps for Windows and Android devices for real time monitoring. A quick search for 'network monitor' should give a variety of options to choose from. Those apps are not regulated by Afrihost so installing software is at the users own personal risk. Personally I use 'Network Monitor Mini' for my Android devices.
Another simple way is to use Windows built in system monitor. This can be accessed from the Task Manager. Pressing 'ctrl+alt+del' will give you access as well as right clicking on the task bar at the bottom of the screen.
I cannot speak for Apple devices so maybe another user can share some insight?