KDDI Corp. said Tuesday it miscalculated e-mail fees for up to 21.03 million cell phone customers because of a technical error that struck before the bills were sent out.
The company said it overcharged 8.67 million customers while undercharging 12.36 million others.
The company discovered the miscalculations after a customer called Saturday to complain about excessive fees, KDDI said.
Although the miscalculations have been estimated to range in the hundreds of millions of yen, the company said it has managed to avoid overbilling any customers.
Miscalculations might have occurred during a 10-day period ending Sunday when errant data were inserted into computers during a system repair, KDDI said.
KDDI will not collect e-mail fees from some 8.67 million customers subject to overcalculation. However, those subject to undercalculation will be asked to pay up.
Depending on the plan, KDDI charges between ¥0.6 and ¥2.3 to send e-mail messages of up to 250 characters.
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