WASHINGTON — For more than an hour, Sheryl Sandberg, Facebook’s high-profile chief operating officer, sheepishly pledged to “do better” — over and over — as stern-faced members of the Congressional Black Caucus grilled her on Thursday about Russian ads aimed at exploiting racial divisions during last year’s election.

For black lawmakers, it was a chance to vent — at the outrage they felt toward Russian intelligence and its efforts to foment racial unrest in the country; at the frustration they felt toward three separate congressional investigations into Russian interference that have plodded on and yielded little; and at Facebook itself, which has been long on promises and short on action.

“She was checking the boxes. She said all the right things,” Representative Donald M. Payne Jr., Democrat of New Jersey, said of Ms. Sandberg. But he was not satisfied. “I had an uncle who hated when you said ‘gonna’: ‘I’m gonna do this, and I’m gonna do that.’ He used to say, ‘Don’t be a gonna.’ And that’s what I said to her, ‘Don’t be a gonna.’”

Facebook’s chief executive, Mark Zuckerberg, after initially denying that Russians had exploited the company’s system, has reversed course and admitted that groups backed by President Vladimir V. Putin of Russia paid Facebook to influence voters last year with ads designed to inflame and exploit racial, political and economic rifts in the United States. Russian-backed Facebook pages promoted anti-immigrant rallies, targeted the Black Lives Matter movement and focused attentions on critical election swing states like Wisconsin and Michigan.