Waiting times on Centrelink's phone lines have improved in the past year; by 26 seconds.

The Department of Human Services confirmed on Wednesday that average waiting times across the welfare agency's 50 phone numbers was 16 minutes and 27 seconds, an improvement from the average of 16 minutes and 53 seconds recorded in 2013-2014.

The performance is considerably better than the time the Australian Greens' calculated on Wednesday - 18 minutes and 42 seconds - which was based on incomplete material provided by the department during its Senate Estimates appearance that day.

The committee appearance came just two weeks after the welfare agency's performance was savaged in an Auditor-General's report that found 26 million callers failed to get through to the welfare agency in 2013-2014.

However, department bosses told the cross-party committee that some report findings were harsh and that many of the 13 million people who hung up before getting through to the Centrelink system might have been satisfied customers.

Department secretary Kathryn Campbell hit back at some of the criticism in the Auditor-General's report, saying it was not clear why there were so many "abandoned" calls and it was possible that people hung up after they got the information they needed from recorded messages.

"We did raise with the Australian National Audit Office that these were very complicated and intricate services to provide," Ms Campbell said.

"The point we tried to make with the ANAO on a number of occasions around what are called abandoned phone calls, is that sometimes it can be that customers have received the information they are looking [for] from pre-recorded messages."