The POCO meter will also measure the losses of the TX, because it measures at the primary ( 11kV) side.
From the 3 readings obtained you can see there is minor imbalance over the 3 phases. The second phase is the lightest loaded. For the 375 kW load that is pretty good, i have seen a lot worse imbalances.
A 1 MVA TX will have an Fe loss and Cu loss of a couple of kW / hr. depending upon loading, which will account for the difference in readings.
The utility metering is done correctly. it looks to me that the building owner (landlord) tries to save some money on CT's and only measure one phase, and multiply the meter readings by 3, in stead of three CT's and polyphase meter.
What type of load do you have ?
Motors or mixed, eg lighting , airco, computers etc.
You could perhaps save a little bit by shifting some single phase loads from the first ( metered ) phase to the second or third phase in your case, although big unbalances on TX's are not the best practise.
