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The Federal Communications Commission said Tuesday that phone and internet provider CenturyLink will pay $550,000 to settle an investigation into a practice known as "cramming": when phone companies add unauthorized third-party charges to customer bills. CenturyLink will also stop billing for most third parties, start refunding affected customer accounts and let customers block future third-party charges.

"Over the years, the FCC has done yeoman's work in fighting cramming and getting major phone companies to stop this practice," Rosemary Harold, chief of the FCC's enforcement bureau, said in a release. "With today's action, another major phone company will stop cramming and prevent unscrupulous third parties from adding fees to bills without prior express consent."

CenturyLink has previously said its own internal investigation found no wrongdoing. The company has faced repeated complaints over issues related to alleged billing fraud, including an ongoing $12 billion class action lawsuit.

In an email to CNET, a CenturyLink spokesperson said the company's policy is to block and refund unauthorized third-party charges that customers receive in their combined bill.

"However, the FCC received some complaints about some smaller third-party providers imposing unauthorized charges on CenturyLink bills. In response, CenturyLink agreed to discontinue its billing service for most third-party providers and make a settlement payment to the FCC," the spokesperson said. "This change will be phased in after appropriate notice to the few providers affected. CenturyLink's billing arrangements with its large strategic partners are not affected."

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Originally published Aug. 13.

Update, Aug. 15: Adds comment from CenturyLink.