Mobile data concern linked to a top-up

Before a recent trip, a refill was added to a phone line with the idea that the extra data would easily last for the planned outings. A few days later, a warning appeared stating that nearly all of the allowance had already been consumed, even though the device had mostly stayed on light tasks like maps and short messages. The usage breakdown in the account view seemed vague, listing broad categories instead of clear app names or sessions. For someone trying to manage costs carefully, this raises worry about hidden background activity or miscalculated totals. What is a sensible way to organize questions so that support can review the situation and explain where the data actually went?