Republican presidential candidate Carly Fiorina attacked "the left and their allies in the media" for a critical report released Monday that says her 2010 California Senate campaign mismanaged money and failed to pay vendors for their work.

More than four years after the failed campaign, Fiorina still owed nearly half a million dollars to 30 entities. She didn't pay off her debt until January of 2015, just a few months before she launched her presidential bid.

One of the outstanding payments due was to her political strategist Joe Shumate who died one month before Election Day as first reported by the Washington Post.

"We projected that there would be debt, and figured we would deal with it after the election," Martin Wilson, Fiorina's former campaign manager, told NBC News.

But Martin added that Fiorina was very slow in dealing with it. "We had suggested several remedies to Carly after the election to discharge the debt. She just couldn't really focus on it, I guess," he said.

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Fiorina dismissed the report, telling reporters Monday afternoon that "all of our debt was paid off and everyone was paid in full" and that she doesn't think "The Washington Post has much credibility anymore."

Her campaign slammed the media for unfair treatment in comparison with coverage of Democratic presidential candidate Hillary Clinton.

"It's becoming obvious that the left and their allies in the media are terrified of Carly because she is everything Hillary (Clinton) isn't — a candidate from outside the political class whose authenticity and grasp of the issues connects with voters because she has the track record to challenge the status quo," a Fiorina campaign aide told NBC News.

Fiorina, who is a wealthy former head of Hewitt Packard, was criticized for repaying herself more than $1.25 million before her staff and vendors — and even before Election Day, Federal Election Committee reports show.

"Just as (California Democratic Sen. Barbara) Boxer was going negative on Fiorina's business record, Fiorina paid herself back a million dollars, starving her campaign of resources and stiffing her staff of half a million in pay," a source familiar with the California senate race told NBC News.

At the end of her $23 million campaign, Fiorina was nearly $1 million in the hole. She did little to pay down her debt between the years of 2013 and 2014, paying just $275. As she was gearing up for her presidential run, in January of 2015, Fiorina did pay off the final $490,000 in outstanding expenditures — four months before she announced her bid for the Republican nomination.

Larry Noble, senior counsel at the Campaign Legal Center, said, "It's not uncommon for a loser to have debt at the end of the campaign."

Hillary Clinton did not pay off her debt from her failed 2008 presidential run where she spent more than $250 million for more than four years. But her $12 million debt was finally retired on December 31, 2012 with more than $70,000 worth of payments to her pollsters' firm, Penn and Schoen.

Mosheh Gains contributed to this report.