Consumers complaining about their mobile service providers is nothing new, but last month, the FCC received more complaints from Verizon subscribers than it had in the previous 8 months combined. After recording an average of 180 complaints a month, the agency received an astounding 2,079 complaints in September.

So what the heck happened in September?

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According to Cleveland’s Plain Dealer, the jump can be attributed to unexplained overage fees, which interviews and figures gathered through the Freedom of Information Act show have affected thousands of users in recent weeks.

“That’s an incredibly large leap,” says Bruce Kushnick, executive director of New Networks Institute. “If the Federal Communications Commission doesn’t investigate what is going on here, something is wrong. This is just the tip of the iceberg. You have to wonder whether this has been done on purpose.”

The Plain Dealer originally began reporting about the rise in complaints on September 9th. Shortly after, a Florida woman came forward with a horror story of her own: she’d received a bill for $9,153 from 569GB of data overages.

As for why so many users are suddenly seeing their data usage spike in recent weeks, there doesn’t seem to be a clear answer. Some say that Amazon apps appear to be sucking up an inexplicable amount of data while others claim that there are glitches in Verizon’s billing process, but no one knows for sure.

Verizon and Amazon both declined to comment on the story when The Plain Dealer attempted to get in touch. Although the number of complaints is still a tiny fraction of Verizon’s 100 million+ user base, it’s still a troubling trend for the carrier. Plus, this is a pretty bad time to be making mobile customers angry.