12/09/2017 4:02 PM AEST | Updated 12/09/2017 4:03 PM AEST

The Bizarre Disappearance Of Chantelle And Leela McDougall, Who Left Town With A Cult Leader 10 Years Ago

It's one of Australia's most baffling missing persons cases.

In July 2007, Chantelle McDougall, 27, told her parents she was going to Brazil with daughter Leela. They haven't heard from her since.

It's been a decade since Chantelle McDougall and her six-year-old daughter Leela disappeared from their small-town home in WA with the shadowy leader of an internet doomsday cult, but parents Cath and Jim McDougall still live with the guilt.

"It's really a big emotional roller coaster that you're on, and you can't get off it," Chantelle's father Jim said, in an episode of SBS program 'Insight' set to air on Tuesday night.

In July 2007, Chantelle McDougall told her mother that the family was going on an extended holiday to Brazil to live in a commune near the Amazon and "help people". They haven't been heard from since.

What ensued was a decade-long search by police, which took them all over Australia and eventually to Brazil, in what has become one of Australia's most baffling missing persons cases.

Mum Cath said she had a "gut feeling" that "something strange was up" during her final trip to see visit her daughter and granddaughter at their home in the sleepy town of Nannup in Western Australia in 2007.

"A passport for Leela had come while I was there, but they didn't say anything about it. Simon took it and put it away," she told 'Insight' host Jenny Brockie.

"I wish I had asked more questions and tried to find out more, but I thought, she's an adult. She's got her life."

At the time of her disappearance, the young mum was living with older boyfriend and leader of a cult called the Truth Fellowship, Simon Kadwell, who was also Leela's father, and fellow cult member, Tony Popic, in a rented fibro home in the sleepy town of Nannup, 270 kilometres south of Perth.

Simon Kadwell, known to his followers only as "Si", had written a book, 'Servers of the Divine Plan', which preached to its "servers" to take up their positions on Earth before the birth of a new world order of higher consciousness at the end of a 75,000 year cycle.

Cath McDougall said Kadwell was "very weird", but she knew little about him as he locked himself in his room whenever she came to stay.

Simon Kadwell, 45 (real name Gary Felton), didn't work and spent most of his time in his room on the Internet spreading information about his doomsday cult, which called on followers to take up their positions on Earth before the new world.

A video Chantelle sent to her parents before she vanished shows the four, all wearing dots on their heads, bowing and saying "namaste", before six-year-old Leela laughs into the camera.

The family rarely entertained, but during Cath's stay in Nannup, they had a visit from mysterious callers, whose identity to this day remains unknown. Cath believes its these visitors who could hold a clue into what happened to her daughter and granddaughter.

Chantelle, 27, was last seen in the neighbouring town of Busselton on July 13, 2007, where she sold her car to a local dealer for $4000 and drove away in a waiting vehicle.

The money deposited into her bank account has never been touched.

At their home, police found dirty dishes, a full refrigerator and a note pinned to the door saying the family were going to Brazil. But Australia's immigration department could find no record that they ever left Australia.

Cath McDougall described her granddaughter Leela, who was six at the time of her disappearance, as "kind and caring", "loud" and "full of life".

In the years that followed, it emerged that Simon Kadwell was in fact Gary Felton, an illegal immigrant who had stolen his pseudonym from a former associate in Britain.

"We found out he had conned people out of all their money and plagiarised the stuff he had written in his books... he was just a conman," Cath McDougall said.

The book 'Servers of the Divine Plan' had sold just 4,000 copies when it was withdrawn from sale by the owner of Esoteric Publishing, Brett Mitchell, following the family's disappearance.

Chantelle's parents travelled all over Australia posting fliers with Chantelle and Leela's photographs in the search for their lost loved ones, but their pleas for information remain unanswered.

WA Police have downplayed any links between Feldman (Kadwell) and the mother and daughter's disappearance, but the McDougalls remain convinced that the elusive conman is to blame.

Their hopes are now pinned on a coroner's inquest into the disappearance and "suspected deaths" of the four, set to take place in December.

Chantelle McDougall, 27, in the bizarre video she sent her parents before her disappearance, along with daughter Leela, 6, flatmate Tony Popic, 40 (right) and partner Simon Kadwell, 45 (back).

Cath McDougall says she still hopes a witness will come forward with new information.

"We have this feeling that someone knows something -- perhaps the friends that came (to Chantelle's house) that night," she said.

"After ten years and you haven't got a lead to find out anything -- it's hard to deal with."

The bizarre case again made headlines in November last year, when a mysterious English-speaking teenage girl resembling Leela was spotted living rough on the streets of Rome.

Leela was six when she disappeared and would now be about 16 years old.

"At first I felt it could be (Leela), but I was pretty sure it wasn't because our granddaughter had a high forehead and this girl did not have a high forehead and I don't think that changes," the girl's grandmother said.

The mystery girl turned out to be Swedish 21-year-old Embla Jauhojärvi, who has Asperger's syndrome and had left her father in Stockholm to study Italian in Rome.

Jim and Cath McDougall with an age-progressed photo of their granddaughter Leela, who would be 16 years old if found alive. A coroner's inquest into her disappearance will be held in December.

"Every time something like this comes up, your hopes get raised and you wonder where they are. It's just horrible."

The McDougalls join the relatives of other long-term missing persons on the program, including the family of Sydney man Sevak Simonian, who was 21 years old when he went missing in bushland in the Blue Mountains three years ago.

Every year in Australia, around 38,000 people are reported missing. Most of them are found within a short period of time, but there remains over 2,000 long-term missing people, including hundreds of children.

The Insight episode Unresolved will air on Tuesday night at 8:30pm on SBS.