When the parents of Phoebe Klebahn, 10, received a "frantic call" from a counselor saying she was not on the flight that was supposed to take her to camp, it took them nearly an hour to find out she had missed her connecting flight. NBC's Diana Alvear reports.

The parents of a 10-year-old girl are not happy after their daughter was left stranded in Chicago, when United Airlines reportedly failed to help her to a transfer flight as she was traveling alone on June 30.

The incident was brought to light this week by Bob Sutton, a family friend and Stanford management professor who writes about workplace issues.

Parents Annie and Perry Klebahn dropped off their daughter Phoebe at San Francisco International Airport on June 30 for her flight as an unaccompanied minor to summer camp, according to a letter dated July 13 to United Airlines. Phoebe was on a United flight that traveled to Chicago and then booked on a connection to Traverse City, Mich.

When the Klebahns received a "frantic call" from the camp that Phoebe did not arrive on her intended flight, they immediately called United and were put on hold for 20 minutes. According to the Klebahns, a United representative finally took their call from India, and only after some back and forth discussion did they finally find out that Phoebe missed her connection in Chicago.

That's because when the 10-year-old landed on-time in Chicago, according to the letter, no one showed up to help her make her transfer flight. Phoebe reportedly asked United attendants in Chicago three times to use a phone to call her parents, but she was told to wait and missed her connection.

"When she missed the flight she asked if someone had called camp to make sure they knew and they told her 'yes—we will take care of it,'" the Klebahns wrote in the letter. "No one did. She was sad and scared and no one helped."

Four hours later, Phoebe did end up making it to Traverse City safely, only after the Klebhans appealed to a United employee who was a mother herself. They were later told by United that the airline outsourced the unaccompanied minor services to a third-party vendor, who "forgot to show up."

A United spokesperson told NBC News on Tuesday that they have reached out to the Klebahns to apologize, and the airline is redepositing the miles used to purchase the ticket into Perry Klebahn's frequent flier account. The airline is also refunding the $99 unaccompanied minor charge.

"What the Klebahns describe is not the service we aim to deliver to our customers," United spokesperson Joe Micucci said in a statement.

The Chicago-based airline did not provide further details of the incident.

An e-mail sent by NBC News to Perry Klebahn was not immediately returned Tuesday morning.

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