I cannot understand any problem with a bill being estimated (although on line one can enter the actual reading and you will be re-billed). Any over estimation or under is automatically corrected when the next actual reading is taken. Of course changes in the actual charge per the units may change and one may be paying a little higher (or even lower) for a few units than with an actual reading.
I monitor my electric account and two others for my non resident sons. I get email notification that the new bill is ready, before it is sent to the bank, and, for me, very simple to understand what is being charged for what.
Just checked an on line bill:-
There is the standing charge,
The units consumed between actual readings
Less or plus, if the last bill was estimated.
The Gov surcharge
Hire of the meter
The total.
The Spanish:-
Facturación
Producto: TUR BT GRAL <= 10 KW
Energía eléctrica
Concepto C lculos Importes
FACTURACION DE LA POTENCIA 4,4 KW x 29 DIAS x 0,056375 EUR/KW Y 7,19 DIA
FACT. CONSUMO LECTURAS REALES 502 KWH x 0,142349 EUR/KWH 71,46
ABONO CONSUMO ESTIMADO -324 KWH x 0,142315 EUR/KWH -46,11
IMPTO.SOBRE LA ELECTRICIDAD.LEY 66/1997 32,54 EUR x 1,05113 x 4,864 %1,66
EQUIPOS DE MEDIDA 29 DIAS x 0,019672 EUR/DIA 0,57
. ___________
. Subtotal 34,77
. IVA NORMAL 18 % de 34,77 6,26
Total Factura
41,03 €