WASHINGTON (CNN) -- A computer error in its billing system led Verizon to overcharge some 11,000 customers in the mid-Atlantic region in June, the company announced Wednesday.

The programming error led to overcharges ranging from $200 to several thousand dollars for some customers in Washington, D.C., Maryland, Virginia and West Virginia, according to Verizon spokesman Harry Mitchell.

The company sends out 5.3 million bills a month in that region.

Verizon discovered the error June 26, one week after the problems began. The company said it will credit affected customers in the next billing cycle.

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