Have you tried a full factory reset? Have you tried simply restarting the device? Have you tried using a different SIM card to see if it will recognize that? We need more info on your end to be able to give you a good answer.
Public Mobile won't be able to provide that information for you. To get that info, you must manually go into your phones Settings, then go to your data settings. There should be a graph showing which apps use the most data.