If you are using task killers like DU Boost, CleanMaster, etc. Some of these task killers, when ""cleaning"" RAM, also stop all background services. So, Accessibility for  >>Mubble<<  is also stopped by them. If  >>Mubble<< Service is stopped by the OS, then the app will not be able to read the pop ups received from Network Provider and hence can't update your balance.To avoid this problem, add Mubble app to the White List of your Task Killer , so that it doesn't turn off Accessibility for >>Mubble<<. Also lock mubble in recent task list.