Nearly 29 million calls to Centrelink got a busy signal in the past year as the welfare agency's performance in answering its phones got even worse.

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 Department of Human Services, which oversees Centrelink, has spent $32,249 on Cellebrite products in the 2016 / 2017 financial year. Credit:Bradley Kanaris

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.