An envoy from an Australian Indigenous group has travelled to Germany to push for a meeting with the head of technology giant Siemens, claiming the company failed to properly check that traditional owners supported Adani’s controversial Carmichael coal project in Queensland.

The Wangan and Jagalingou Family Council, which has spent years challenging the Adani mine, says the company was wrong to claim the project had been approved by its people.

W&J council representative Murrawah Johnson, who is in Germany, has asked to meet Siemens’ chief executive, Joe Kaeser, and will attend the company’s AGM in Munich on Wednesday.

The company is standing by its earlier statements about Indigenous support for the project, telling Guardian Australia on Tuesday that it had taken its position from the “prescribed legal process in Australia”.

Also on Tuesday, 19 health groups advocating action on climate change from countries including Australia, the UK, US and India, published an open letter to Siemens, asking the company to “end its association with Adani and its climate-wrecking coalmine”.

In January, Siemens said it had reviewed its reported $30m contract to provide signalling technology to the mine’s railway, and that it would complete the work.

Kaeser said the Carmichael project was “approved” by the W&J people which, he said, was “very important to us”.

Johnson said: “It is ridiculous that Siemens could say that W&J people support this mine. We’ve had three meetings that have all said no.”

Construction has started on the mine, from which coal will be taken by rail to the company’s Abbot Point port for export to coal power stations. The mine is one of the most contentious resource projects in Australian history.

The project has also caused rifts between Indigenous people. Some support the mine, while others, including W&J council leader Adrian Burragubba, are strongly opposed.

Speaking to Guardian Australia from Munich, Johnson said “free, prior and informed consent” – a cornerstone of negotiations between First Nations peoples and project developers – did not exist for the Adani mine.

She accused Siemens of relying on “talking points” from the mine’s supporters, incuding former resources minister Matt Canavan, the Queensland government and Adani itself, rather than hearing directly from traditional owners.

The outcome of one April 2016 meeting that voted strongly in favour of an Indigenous Land Use Agreement has been consistently used by Adani supporters. But Johnson and others describe that vote as a “sham”, claiming it had been boycotted by some W&J people.

The W&J council was established in 2014 as a “self-determined” representative group of 12 family lines, partly out of frustration with the native title process and to advocate against the Adani mine.

In 2019 the state government extinguished native title over Wangan and Jagalingou country to enable the Adani project to proceed.

The W&J council has written to Siemens and provided legal advice it commissioned from the US-based environmental law group Earthjustice.

The letter says: “Contrary to statements by the Adani corporation and members of the Australian government, we have never given our free, prior and informed consent to the extinguishment of our rights, or the development of the Carmichael mine on our traditional lands – a development that would destroy large parts of our ancestral homelands to which our law and culture are deeply connected.”

Siemens has said it is one of the first major companies to have pledged to be carbon neutral by 2030.

In a statement the company said: “Siemens’ comment regarding the support of the W&J people refers to the prescribed legal process in Australia regarding Indigenous Land Use Agreements (ILUAs).

“This includes the fact that an Indigenous Land Use Agreement was registered in the National Native Title Tribunal and that the vast majority of the W&J people decided in favour of the Indigenous Land Use Agreement with a vote of 294 to 1. All on public record. Also, further assessment and the ruling of the Full Court of the Federal Court of Australia.

“It’s important to note that in addition to the W&J ILUA, there are other ILUAs covering the project area with three different indigenous groups. These were signed some time ago with the Jangga People, the Birriah People and the Juru People.

“The Siemens signalling equipment for the rail line is designed for safe and efficient operation of trains: trains being delivered by another company on a rail line being built by another company, for a project that was legally and environmentally approved several months ago, where extensive works began several months ago and where over $700 million of contracts have already been awarded.”