“Any of those stupid charges, they’re going to take them right off,” Ms. Burns said in the video.

Ms. Zavala remembered that advice a few days later when she was going over her bills. She decided to give it a shot. “I thought, you know, what could I lose doing it?” she said. “And so I called and I let them know who I was, and I just asked for an itemized bill for that hospital visit.”

About two weeks later, her itemization came in the mail. She opened it and saw that her balance had been reduced to zero.

“I couldn’t believe it, that it was just gone,” she said.

It was unclear whether her phone call was the reason for the reduction. Ms. Zavala’s itemization showed that the hospital had applied “financial assistance” to her debt in September. But Ms. Zavala said she had never asked for assistance and didn’t know it had been applied, even though she had checked her balance in October.

The health care system that administers the hospital Ms. Zavala visited said in a statement that it offers flexible, generous financial assistance programs, and that people who apply for them are typically notified in writing within two weeks of the eligibility determination.

Ms. Zavala shared her experience in a tweet that racked up hundreds of comments, tens of thousands of shares and hundreds of thousands of likes, and Ms. Burns’s video was covered by Business Insider and other news outlets. Many who commented on social media said that a call to the billing department — in some cases to ask for budget assistance — had worked for them or their friends.