Verizon Wireless says about 15 million of its subscribers will receive refunds for mistaken data charges that have cost its customers tens of millions of dollars.

The FCC confirmed reports that it has been investigating the matter for the past 10 months after it received consumer complaints about “mystery fees” on their bills.

“We discovered that over the past several years approximately 15 million customers who did not have data plans were billed for data sessions on their phones that they did not initiate,” said Mary Coyne, Verizon Wireless deputy general counsel, in a statement yesterday. “The majority of the data sessions involved minor data exchanges caused by software built into their phones; others involved accessing the web, which should not have incurred charges.” 

Coyne said most customers will receive credits in the $2 to $6 range in October and November, but cautioned that “some will receive larger credits or refunds.” Customers affected by the refunds would normally have been billed $1.99 per megabyte for data accessed from their handsets. Total refunds could cost Verizon up to $90 million.

FCC Enforcement Bureau chief Michele Ellison suggested Verizon should have moved faster to address customer complaints over billing and said the agency was considering “additional penalties” to ensure companies prioritize the interests of consumers when billing problems occur.

“We’re gratified to see Verizon agree to finally repay its customers. But questions remain as to why it took Verizon two years to reimburse its customers and why greater disclosure and other corrective actions did not come much, much sooner,” Ellison said.

Verizon says it issues credits to customers based on “regular review and monitoring.”

“When we identify errors, we remedy them as quickly as possible,” Coyne said. “Our goal is to maintain our customers’ trust and ensure they receive the best experience possible.”