NB phone apps such as Hugo and Loop can monitor the exact Smart Meter usage by the half hour i.e. the modern smart meters seem to transmit their data to a central database, and your supplier pulls the data from there, as can Hugo/Loop.
This gives you the data, if you record it, to challenge your elec supplier if required. As others have noted, the suppliers are slow / inconsistent at recording and displaying it, albeit the bills seem right (with eOn). In fact it was eOn being useless at displaying the usage who recommended the Loop app. Hugo I find better since it is kWh to 2 decimal places, not 1.