preparation of electricity bill and its distribution to the consumer is faulty. The meter reader notes the meter, prepares the bill there itself , but does not deliver it to the consumer. In my Residential Complex, which has 10 blocks of G+3 floors, he just leaves the bills near one of the meters unguarded. Quite often these blow away in wind and get lost.
The reading is not taken on a fixed date(+- a day). The uneven cycle of taking readings makes the bills unusually high in certain months.