Welcome to the community!
Could you please provide information if you are on a prepaid or postpaid plan.
Could you please verify that your data settings on your phone doesn't limit the whole quantity of data available on your plan - there is usually such settings that you can limit in amount of data and in timing the data look under settings.
Could you please verify that hotspot isn't turned on which would leak your data use over other devices.
Could you please confirm you currently use the last updated Fido app.
Are you the originated phone/ plan owner?
Please provide additional information in order to assist you should you still require we'd be happy to help, don't hesitate.