The agency's parent department told Senate Estimates on Thursday night that another 7 million calls had been "abandoned" with customers not prepared to wait any more to have their calls taken.

The previous year, about  22 million phone calls to Centrelink went unanswered, with the welfare agency blaming emergencies and a complex payment system for its worsening performance.

The Human Services hierarchy were at pains to stress on Thursday night that the figures did not mean that 29 million individual customers had received engaged tones.

Department Secretary Kathryn Campbell said smartphones were enabling customers to call back 70 or 80 times in rapid succession.

Greens Senator Rachel Siewert, a member of the committee who heard Thursday night's evidence from senior Department of Human Services bureaucrats, said phone lines remained a major cause of frustration for Centrelink customers.

"In addition, call waiting times on the main program phone lines remains high causing further frustration," the West Australian Senator said on Friday morning.

"I have been tracking this growing problem for some time and every estimates the numbers seem to continually climb.

"It is clear the issues with the phone service for Centrelink has not been adequately fixed.

"Although the department says it is trying to reduce the problem, there is only so much they can do on available funding.

"Whilst the government likes to vilify people on income support, people are trying to do the right thing and to adjust earnings, and other details or trying to gain urgently needed support.

"The government must address these flaws".

Ms Campbell also told the committee that a call being "abandoned" before being answered was not necessarily a bad thing.

"I'll just flag the definition of abandoned because abandoned sounds like that might be a negative outcome [but] sometimes a customer might receive the information they need from the recordings and choose to exit the queue," the DHS boss said.

The department said that 47 per cent of customers who hung up, did so in the first five minutes of being on hold.

"We haven't determined if that's a good abandoned or a bad abandoned and I just wanted to make sure that people got that," Ms Campbell said.

Centrelink says it has brought down the average time to answer its social security and welfare services phone lines to 15 minutes and 9 seconds in the past financial year, according to the Human Services annual report.

But the committee heard on Thursday that some lines were clocking up average wait times of more than 25 minutes.

Senator Siewert told the departmental boss she thought the "average" figure was misleading.

"Ms Campbell, it's very misleading for you to sit there and say average wait time was whatever it was when its going on for half-an-hour for youth and students," the senator said.