The Social Security Administration overpaid her. Now she owes $35,000.

A Social Security recipient in her mid-70s says she received an unexpected bill for $35,000 after the U.S. Social Security Administration allegedly overpaid her benefits for four years.

The woman, who spoke anonymously to CBS News because she feared retaliation while appealing the decision, said her monthly benefit suddenly dropped by about $600 in February. After taxes, voluntary withholding and Medicare deductions, she was left with about $2,700 a month.

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I started calling Social Security to figure out what happened and [to share] why I was upset about it.

She said she began calling the agency to ask what had happened and explain why she was upset. A letter reviewed by CBS News said the reduction corrected her benefit amount, but the woman said it gave no further explanation. In August, the agency sent a notice saying it had overpaid her tens of thousands of dollars, covering the period since she began claiming her own benefits.

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I’m alarmed.

The letter gave her 30 days to repay the full balance. If she could not, the agency said it would reduce her benefits by 50% for two years starting in December, leaving her with about $1,350 a month. “I’m alarmed,” she said. “I’m trying to sort out what I should do next at this point because I was already underway with a plan.”

The Social Security Administration did not immediately respond to CBS News’ request for comment. The agency told the program “60 Minutes” last year that it sends overpayment notices to about 2 million people annually across its benefit programs. Its website says overpayments can result from missing or incorrect information, including unreported changes in income or marital status. Recipients may still face repayment demands even when they report changes, according to Nancy Altman, president of an advocacy organization.

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I’m trying to sort out what I should do next at this point because I was already underway with a plan.