"We said, 'Whoa, what's happening,'' Vivian Ho of San Jose said of her shocking bill. "How could that happen? We almost fainted."
Even her carrier, T-Mobile, said it was a bit of a mystery as to how a family could use all that data -- nearly 900,000 megabytes -- during a short time on the day they flew into Vietnam.
Chung's son Nicholas admits he was playing video games during the flight -- but only "offline" games that do not require an internet connection. And he said he is sure the phone was set on Airplane Mode for the entire trip. That setting blocks any internet access.
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"It would be pretty unusual, when you have airplane mode on, to incur any data charges,'' said Jessica Dolcourt, cellphone expert at CNET Interactive in San Francisco.
A possible explanation? Dolcourt said it can be very easy to mistakenly turn off the safe setting. Just one touch of a button turns Airplane mode on -- but the same quick touch turns it off.
"It's a lot easier to accidentally turn off Airplane Mode when you're turning on another control on your phone,'' Dolcourt said. "If you think you're pressing the Wi-Fi button for example and you hit (Airplane Mode) instead, and you don't realize it, and you don't turn it back on.''
It means you are leaving the phone open to accessing a data network.
She advises instead to turn off all cellular data by using the apps on the settings page. The process for iPhones is slightly different than for Android phones.
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"You can turn off all cellular connections and that's just a best practice to make sure you're never going to incur any of those charges," she said.
But even if Nicholas accidentally switched his phone out of Airplane Mode, Dolcourt said it would take a lot of activity to use 900 megabytes of data.
"Uploading takes a lot of data, downloading, streaming a movie, navigating on Google maps takes a ton of resources,'' she said.
But not playing offline video games.
T-Mobile tried to track down how that data was used, but said it had limited information. In part, that's because the data was provided by T-Mobile partner Viet-Tel, a Vietnamese mobile data company.
At first, T-Mobile agreed only to reduce that $13,000 charge. But after 7 On Your Side contacted the company, T-Mobile canceled the entire bill, saying it was obvious Nicholas didn't intend to use all that data.
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His mother was ecstatic.
"On that day I was so relieved, I said yeah!" Chung said, laughing. "I'm so glad 7 On Your Side is here to help us."
Here's how to fix your phone so you don't end up getting charged!
- For data information for Android phones, visit this page.
- For data information for iPhones, visit this page.
For more stories, photos, and video from 7 on Your Side and Michael Finney, visit this page.