Centrelink clients trying to get through to the welfare agency's telephone lines have hit engaged signals an "astronomical" 28 million times in just seven months.
The figures, revealed in Senate Estimates on Thursday, mean Centrelink is track to almost double the amount of calls it blocks this financial year.
The Greens are furious at the further deterioration of the troubled agency's customer service effort, saying the government now had no choice but to do something about the "broken system".
Centrelink blocks calls to its overworked telephone lines if they are already jammed, a practice it says saves callers having to spend many minutes, and sometimes hours on hold.
But the Greens say the exploding numbers of blocked calls represent failed attempts by "exasperated and struggling" citizens to contact their government.
The numbers of engaged signals have exploded in the first half of 2016-2017, nearly equalling those of the entire previous year, bosses from Centrelink's parent-department, Human Services, told Estimates in Canberra on Thursday.
More than 29 million calls were blocked in 2015-2016, a large increase on the previous year when Centrelink excluded 22 millions calls from its system.
More than 4 millions calls have been "abandoned", where customers simply give up and hang up the phone, since July 2016, again putting Centrelink on track to outstrip its 2015-2016 total of 7 million.
The department has said in past that an abandoned call was not necessarily a bad thing because the caller may have got the information they wanted from the recorded messages played while they waited on hold.
Centrelink's customer service effort has been under increased scrutiny for several years, reaching a low point in 2015 with a scathing official audit that found Australians spent 143 years waiting in vain to speak to Centrelink the previous year, before simply hanging up.
Official Centrelink policy is to encourage clients to contact the agency using the myGov portal or one of its smartphone apps but the online effort has been beset by glitches, failures and complaints.
But reports indicate that myGov in particular has been performing better in recent months after improvements were made.
Human Services, the government's largest department, is also facing an intensifying backlash over its controversial "robo-debt" program and a bitter industrial dispute that has been raging since 2014 over conditions and wages for its 36,000 public servants
But there was better news in Estimates on Thursday about on average waiting times on Centrelink's phone lines, with the average speed of answer 14 minutes and 10 seconds against a target of 16 minutes.
Greens Senator Rachel Siewert, who has pursued Centrelink over it performance for several years, expressed exasperation on Thursday over the increase in busy signals.
"Twenty-eight million calls hitting a busy signal in the first seven months of this financial year is astronomical and could reflect people trying to get through to fix an incorrect debt", Senator Siewert said.
"To see 28 million busy signals in the first seven months shows an extreme trajectory that the Government must work to remedy immediately.
"Behind those 28 million attempts are exasperated and struggling Australians.
"It should not be this hard to access Centrelink, the Government should wake up to how broken the system is".
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