You are charged for the energy consumed by you, in terms of KWH. Capacitors just do not contribute to KWH, they take reactive current , or reactive power. At house loads, any losses in cables and wires are negligible, so there is no question of reduction of power on this account.
Some unscrupulous elements take advantage of ignorance of public at large, and have been selling so called power savers using small capacitors. They are simply looting the people.
Power capacitors do help in industry, where loads are heavy and low power factor is penalised. In these loads, power capacitors can save energy bills considerably by improving the power factor, as also reducing line and cable losses.
Source: Quora
