Verizon Facing FCC Questions on Data Metering After $9,100 Phone Bill by @FortuneMagazine September 17, 2016, 3:36 PM EDT E-mail Tweet Facebook Linkedin Share icons The Federal Communications Commission confirmed this week that it is examining complaints about data billing from Verizon Wireless customers. The move comes after a series of stories in the Cleveland Plain Dealer detailing unexplained— and in some cases, inexplicable—upticks in customers’ mobile data usage. The Plain Dealer’s stories were mostly authored by Teresa Dixon Murray, whose reporting on similar billing issues led to a huge fine against Verizon in 2010. Murray first wrote about mysterious increases in her own family’s data usage, caused in part by data apparently being used while the family slept. Get Data Sheet, Fortune’s technology newsletter. In response to that first story, Murray received a torrent of tales from readers across the country with experiences that were similar, or even stranger. One Verizon customer told Murray that she was being charged for wireless data—despite using a flip phone with no wireless data connection, on an account that blocks data. Another customer, Joyce Shinn, had been using her recently-deceased husband’s phone to answer phone calls to settle his affairs. About a year after his death, the phone suddenly started showing data usage, triggering overages on Shinn’s account. Many more accounts came in from customers detailing incremental rises in data usage over the course of several months, despite no changes in their usage habits. The capper came from a Tampa mother, Valarie Gerbus, whose data usage suddenly surged from less than 4GB one month to 569GB the next, resulting in $8,535 in data charges. Verizon charged her an extra $600 when she decided to cancel her plan. Verizon did ultimately agree to waive much of that bill, and in a statement said they had resolved Gerbus’ situation “to her satisfaction.” But the company provided no details about the nature of the initial problem. For more on wireless, watch our video. Various Verizon spokespersons speaking to Murray attributed the problems to, essentially, consumer error. Mysterious increases in data usage may have been caused, they said, by a feature called Wi-Fi Assist, which switches phones to a mobile network when a Wi-Fi connection seems poor. Other possible culprits included push notifications, which always use the wireless network rather than Wi-Fi. These are ultimately anecdotal stories, and anyone with a cell phone plan knows how tough it is to be disciplined about data usage. But as Murray’s previous run-in with Verizon shows, what looks like a scattering of isolated incidents can sometimes add up to something much bigger.