The corruption investigation into former Australian Border Force head Roman Quaedvlieg is still going more than three months after he was sacked.

The Australian Commission for Law Enforcement Integrity confirmed the investigation is continuing in comments to the ABC on Wednesday, but Quaedvlieg has hit back. He has denied corruption allegations and suggested the agency is merely finalising its report rather than actively investigating him.

On Wednesday the opposition leader, Bill Shorten, said Australians were “all in the dark about what’s happening” with the investigation and the case “highlights the need” for a national anti-corruption commission, which Labor has proposed but is being resisted by the Coalition.

The governor general sacked Quaedvlieg in March for misbehaviour, including making a “wilfully or recklessly false statement” about his relationship status and modifying policies to advantage a candidate for recruitment.

The findings related to allegations he helped a junior staff member with whom he was in a relationship get a job at the Sydney airport.

In March the attorney general, Christian Porter, made a recommendation after receiving a report from the department of prime minister and cabinet, but on Wednesday the ABC reported a separate investigation by the commission had not been finalised.

“The integrity commissioner received a notification in relation to Mr Quaedvlieg … in June 2017 and commenced a corruption investigation shortly thereafter,” a commission spokesman reportedly said. “At this time, the investigation remains ongoing.”

Quaedvlieg defended himself on social media by arguing that “finalising a report is different to ‘still under investigation’, as much as the latter may be an expedience to reject [freedom-of-information] applications”.

“My position has not changed – I deny the allegations; I’m frustrated at the time the entire process has taken; and I’m considering legal options,” he said.

Finalising a report is different to ‘still under investigation’, as much as the latter may be an expedience to reject FOI applications. My position has not changed - I deny the allegations; I’m frustrated at the time the entire process has taken; and I’m considering legal options https://t.co/zEHT38pF2b — Roman Quaedvlieg (@quaedvliegs) July 3, 2018

Quaedvlieg also reportedly said he had “never been interviewed by anyone, including ACLEI”.

The commission’s spokesman said an investigation remained ongoing until a final report was provided to the attorney general and the relevant law enforcement agency.

“The attorney general has not received a final report from the Australian Commission for Law Enforcement Integrity in relation to this matter,” a spokesman for Porter said.