One of the Federal Government's most criticised departments was told to abandon its performance targets as there was no realistic chance they would be met.

Key points: Centrelink has been heavily criticised for debt recovery program

Centrelink has been heavily criticised for debt recovery program Approval levels have been slipping since 2012

Approval levels have been slipping since 2012 Poor results prompt PwC to pay for review into success and performance

But the advice, commissioned from consultancy firm PricewaterhouseCoopers (PwC) at a cost of $150,000, was rejected by the giant Department of Human Services (DHS), which has not come close to meeting its 85 per cent customer satisfaction goal for Centrelink in years.

That may not be a surprise given more than 42 million calls to Centrelink received an engaged signal during the first 10 months of this financial year.

That compares to almost 29 million in the 2015-2016 financial year and 22 million the year before that.

The agency has been heavily criticised for its debt-recovery program this year, but approval levels have been slipping ever since a peak at 71 per cent in 2012-2013.

The poor results prompted senior officials to pay PwC for a 16-week review of how it measured success and performance.

The firm's report to the Government, obtained under freedom of information laws, told the DHS they would not succeed without "substantial change to the customer and service experience".

Instead, the consultants told the Government to consider abandoning the target in favour of more reasonable and achievable goals.

"It's clear that a target of 85 per cent will not be achieved under all models for Centrelink without substantial change to the customer and service experience," the report said.

"Consideration could be given to revising the KPI [key performance indicator] target to be in line with other global welfare providers and to be achievable based on historic performance."

Medicare vs Centrelink customer satisfaction KPI. ( Supplied: Department of Human Services )

Centrelink satisfaction low

The department relies on voluntary surveys and PwC offered alternative measures to avoid bias, which were rejected.

"No decision has been made to make any changes," DHS spokesman Hank Jongen said.

"Given that many people accessing welfare are experiencing difficult circumstances, the customer satisfaction targets intentionally set a high bar."

The consultants also warned the lofty goals might undermine performance, leading to a lack of ownership and accountability within the department.

"Unattainable targets can result in motivation and performance decreases while increasing risk-taking behaviours," the report said.

The department's upcoming performance figures, to be published in the 2016-2017 annual report, will likely be affected by the backlash against the debt-recovery program.

An ombudsman report into the program found it had treated some customers unfairly and there were numerous deficiencies in service delivery and communication with the public.

While satisfaction with Centrelink remains low, approval for Medicare is consistently higher.