Australians spent 143 years waiting in vain to speak to Centrelink in 2013-2014, before simply hanging up, the auditors calculated.

About 13.7 million calls did not even make it to the point of being put on hold, after they were blocked or received a "busy signal".

Another 13 million of the calls that did manage to get into the system were "abandoned", with the callers getting tired of waiting to speak to an operator, the Audit of the Department of Human Service's "Smart Centre" system found.

Lengthy waits for Centrelink telephones to be answered is the number one complaint against the welfare agency, and the audit found the problem growing much worse.

Average waiting times have blown out dramatically from just over 3 minutes and 5 seconds in 2010–2011 to nearly 17 minutes 2013–2014.

The auditors blamed a dwindling number of public servants answering telephones, the "performance and reliability" of other customer service channels and a much lower proportion of calls being blocked before they entered the system.

The Auditor's reported that the "average" wait time that Centrelink reported to the government of nearly 17 minutes did not reflect the true experience of many customers, with 30 per cent waiting on hold for 30 minutes or more before their inquiry was answered.

On the positive side, the Auditor-General's office acknowledged that the department was making progress in revamping its customer service and moving tens of millions of transactions each year online.

But the auditors questioned why the giant department could not follow the lead of other government agencies, like the Tax Office, and give callers a more realistic idea of how long they might be waiting.

"Of the 56.8 million calls made to Centrelink 1800 or 13 telephone numbers in 2013-14, 43.1 million calls were able to enter the network while 13.7 million calls were unable to enter the network, that is, the calls were blocked and the callers heard the 'busy' signal," the report says.

"Of the 43 million calls in 2013-14 that were able to enter the network, around 45 per cent were answered by a service officer and around a quarter were resolved in the interactive voice response system."

But the audit office estimated the remaining 30 per cent, about 12.9 million phone calls, were simply abandoned.

In its defence, Human Services said that it must work with the resources it is allocated and estimated it would need to hire 1000 new public servants, at an annual cost of $100 million, to bring average waiting times down to five minutes.

But the auditors found the department's performance did not stack up well against that of other departments.

"The current target does not provide a clear indication of the wait times Centrelink telephone customers can generally expect, due to the distribution of actual wait times around the 'average'. Centrelink customers also continue to experience high levels of call blocking and call abandonment, which can further impact on the customer experience," the report says.

Community and Public Sector Union national secretary Nadine Flood said the report's findings showed job cuts amid rising demand had put pressure on staff and impacted services.

"This is what years of so-called efficiency dividends that cut jobs looks like – longer wait times for clients and more stress for the staff who are on the receiving end of frustrated clients waiting longer."

Ms Flood said almost 5000 jobs had been slashed from the department's call centres and in-face service centres over five years, as staff answered roughly three million extra calls a year.

"It's unacceptable and it's high time that the government and Human Services fund agencies like Centrelink properly to allow staff to do the job to the level the community expects."

This article originally appeared on The Canberra Times