SAN FRANCISCO (CBS SF) – A lot of us are uploading, downloading and playing games, racking up a ton of data usage. But $555 in a single month? One couple says it isn’t possible.

The couple says they normally use less than 10 gigabytes a month, but their November bill shows that they used more than four times that – 45 gigs. That’s like streaming music for two months straight, or watching YouTube videos for 15 days straight.

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“We didn’t do it,” says Teri Wells.

Verizon agrees that 45 gigs seems like a lot. They took a closer look at Dave and Teri’s bill and credited them for all of the data, blaming it on “phantom usage,” data drained by apps or alerts you aren’t aware of.

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To avoid Phantom Usage Verizon suggests setting your phone to automatically connect to a secure WiFi network when you arrive home or at work and use WiFi for downloads whenever possible.

Dave has now installed an app that tracks data use in hopes of avoiding big bills in the future.

Most cell phone companies allow you to sign up for alerts if you’re about to go over your data. And parents, you may want to monitor your kids’ data. Family plans are can lead to unexpected data overages.

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When using public WiFi networks, always use secure websites that start with “https.”