Updated

Telecom giant Verizon Wireless has agreed to pay a record $25 million to settle allegations it charged customers millions of dollars in "mystery fees," the U.S. Federal Communications Commission (FCC) said Thursday.

Verizon Wireless will also refund at least $52.8 million to more than 15 million affected customers, the FCC said.

The settlement was the largest ever reached in FCC history.

“Today’s settlement requires Verizon Wireless to make meaningful business reforms, prevent future overcharges, and provide consumers clear, easy-to-understand information about their choices," FCC's Enforcement Bureau Chief Michele Ellison said in a statement.

The FCC began investigating Verizon Wireless in January after large numbers of consumers complained of unexplained data charges. The investigation focused on “pay-as-you-go” data fees -- charges of $1.99 per megabyte that apply to Verizon Wireless customers who do not subscribe to a data package or plan.

The investigation found that approximately 15 million “pay-as-you-go” customers may have been overcharged for data usage over the course of three years, from November 2007 to the present.