The Human Services Department has said its phone waits and engaged signals are dropping, while clients are also complaining less about its contractors than its public servants.

But Centrelink officials said clients dealing with private operators contracted to answer calls to the agency were waiting weeks for simple problems to be resolved after receiving the wrong information.

Staff have said some welfare recipients are calling up to eight times to have their questions answered as they deal with private call centre operators.

Their accounts undermine claims from the minister overseeing the welfare agency, Michael Keenan, using a secret report to laud contractors for answering more calls, taking less down time and fewer sick days than public servants.

Nearly 3000 call centre contractors will answer Centrelink calls by April as Human Services escalates its use of private operators while shedding its own staff.

Contractors answering calls most often transferred them to public servants to resolve problems raised by clients, an official said.

The department denied this, saying for the main phone lines contracted private call centres were tasked with, call transfer rates were in line with the department’s wider workforce.

Private call centre staff may have improved at answering questions after time on the job, but were making errors as they grappled with welfare policy and rules that were hard for outsiders to interpret, a public servant said.

"It's not a good model to deliver correct, accurate and timely services," the official said.

"There's a lot of Human Services staff who are responsible for fixing a lot of the problems."

Despite Coalition claims that contractors were cost-effective, the department had up to 50 internal, mid-ranking staff supporting the contractors full time, the Human Services official said.

The Coalition's resort to contractors created more government expense as department staff flew across the country to support private call centres. Repeated phone calls from clients receiving incorrect advice added to government spending.

"There's a lot of hidden costs they are not being open and honest about.

"It's people's lives we're talking about." Problems resolved in calls to Centrelink could be the difference between having enough money to eat, and struggling to afford food.

Human Services Minister Keenan's praise in October for contractors had demoralised many of his department's staff, an official said.

Department spokesman Hank Jongen said Human Services rejected the staff claims about contractors.

There were fewer complaints about contractors than the department's overall workforce, he said. External providers received 0.08 complaints per 1000 calls compared to 0.13 complaints per 1000 calls for departmental staff in its call centres.

"The customer satisfaction result for calls answered by external providers is also comparable to the result for departmental staff," Mr Jongen said.

"We expect to see further call performance improvements once all the additional staff are on-board."

Mr Jongen said average wait times across all department phone lines dropped compared to the same time last year. Call transfers were down 23 per cent and busy signals were down 41 per cent.

"The fact is our service delivery partners are making a very positive contribution towards reducing wait times and busy signals and improving outcomes for customers."

The department is monitoring the contractors' performance, and keeps two or three staff on site once the private call centres are operating fully.

Mr Keenan last year said a $53 million pilot involving 250 Serco call centre workers had reduced the number of calls meeting engaged signals. Blocked calls to Centrelink previously reached 55 million at their peak in 2016-17.

The Coalition in April promised 1000 contractors at a cost of at least $200 million, and later an additional 1500 in August, bringing the total to 2750.