(CNN) Frenchwoman Nathalie Haddadi suffered every parent's worst nightmare: the loss of her child. But instead of sympathy, she says she was punished for her son's crimes as a foreign fighter in Syria.

Haddadi's son, Belabbas, was 21 when he was killed in 2016. His mother says she had tried her best to get him help and bring him home.

In doing so, Haddadi, 43, a non-practicing Muslim, found herself at odds with French authorities; earlier this year, she was sentenced to two years in prison for financing terrorism by sending him money. She is now appealing against her conviction after being sentenced in September.

Her lawyer says the French justice system is making an example of Haddadi to try and dissuade other families from stepping in to try and help relatives caught up with extremist organizations.

As ISIS loses its grip on parts of Syria and Iraq, more and more former jihadist fighters are fleeing, but their parents fear they may receive the same treatment as Haddadi if they try and help their children return.

'Your son died a martyr'

As a child, Haddadi says her son was sporty, chatty, and always surrounded by friends: "Never would we have believed that one day, this would be his destiny in the end."

But by the time he was in his late teens, he found himself in trouble with the police. Jailed for drug dealing and other offenses, Haddadi says Belabbas was radicalized while in prison. When he was released, she says, "it wasn't him anymore."

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She sent him to stay with his father and family in Algeria, but after a few months there he traveled to Malaysia, where he told her he had been attacked by a gang.

"They took his money, and while trying to defend himself he was stabbed in the arm," Haddadi says. "And so, I sent money, I sent altogether 2,800 euros in several transfers."

She says it was at this point that she became worried, and tried to convince her son to return. In response, he shut her out: "He told me, 'That's it ... I've had it.'"

"If I could go back to that moment, I wouldn't be as stern as I was. I would be gentle with him. I would say, don't worry my son where are you? I'm coming. I would book my ticket, I would go get my son and he'd be alive."

Instead of returning to France or Algeria, Belabbas traveled to ISIS' so-called caliphate.

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Haddadi says he called her once he had arrived, saying: "...I'm sorry, I love you but I love Allah more. I have a duty; I am here to help Muslims."

In a second conversation, a month later, she says she sensed he was already becoming disillusioned: "I felt that he wasn't speaking with ease, that he wasn't alone. He told me, 'Mom, there are horrors here.'"

And then, in August 2016, a third call — this time from someone she did not know — telling her: "Congratulations, your son has died a martyr."

"It's a double sentence," Haddadi says. "I can never be in mourning, simply because, you cannot go into mourning if you don't have a body ... if you don't know the circumstances of his death.

"I just want them to let me cry over my son with dignity, leave me to it ... (but) in addition to all this, you have a trial case on your back. It's not over, my troubles are not over."

Conversion to Islam

Authorities in France believe around 500 French citizens are currently in ISIS territory: men, women and children whose numbers have dropped as the war against ISIS has gathered pace, leaving foreign fighters and their families among the dead.

Sylvie, who asked CNN to withhold her identity because she fears for the safety of her family, is another mother living in fear of a call from a stranger in Syria, bearing bad news.

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Her daughter and three grandchildren are among those still thought to be in the country; she says she is desperate to bring them safely back to France, but claims there is no official organization to turn to for advice. She says helplines provided by the government have proven useless, and no one seems prepared to help. CNN reached out to France's interior ministry for comment, but got no response.

Sylvie says her daughter is a victim of brainwashing and indoctrination who deserves sympathy and understanding, not condemnation. "She was introduced to Islam in our society ... we didn't know there was any danger."

After converting to Islam as a teenager, Sylvie says her daughter became more devout, and more removed from her family, as the years passed. She dressed more modestly, stopped eating pork, and even stopped celebrating birthdays.

"In the beginning ... she lived a moderate religion, like many other Muslims in our city," says Sylvie. "Then she started wearing the veil and that was a shock."

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When her daughter met a new partner via a social networking site, and moved across the country to be with him, Sylvie says the radicalization began. Her daughter swapped her headscarf for a full niqab, and sold off all of her possessions, before leaving for Syria with her young family.

Sylvie says her daughter has tried to protect her from the worst of their experiences. "She always sent photos with the kids playing, she would say she was going to the park, one would get the impression they were living in a normal society ... where everything was just fine," she says.

But when she spoke to others who had made it back from Syria, Sylvie says she learned the truth.

"(They would) say 'No ma'am, your daughter is lying -- we wouldn't eat meat for over a year, it's difficult to find water, everything is in ruins.' My daughter would tell me she'd go to the swimming pool, (but) the girls would laugh and say 'Ma'am there are no pools."

Threat of arrest on return

As ISIS' fortunes have waned, more foreign fighters have shown a desire to come home, but authorities in Europe and elsewhere have struggled with how to deal with them.

Many of those who have managed to make it back, traveling the same routes as migrants and refugees, across the Mediterranean, have faced arrest and prosecution on their return

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But UK lawmaker Rory Stewart last week said British extremists fighting with ISIS posed a "serious danger to us all," telling BBC Radio 5 that "the only way of dealing with them will be, in almost every case, to kill them."

Sylvie says the foreign fighters' families can't simply be left to die as ISIS is beaten into submission. "In our society and (with) the powers we have, it seems aberrant that we can kill all these children and these women."

"Even if they must be judged or punished, until (it is) proven otherwise, they didn't kill anyone, they're not the enemy, they're not planting bombs," she says.

Nathalie Haddadi agrees that more must be done to help those who, having made a mistake in traveling to Syria, now find themselves trapped there, before it is too late.

She says a mother's love is unconditional; it can't simply be switched off if he or she takes the wrong path through life.

"When you hold up a little thing weighing three or four kilos, do you sign a contract with it?" she says. "Do you say, 'If you behave, I'll love you until the very end? If you misbehave, then I'll stop loving you?'"

"That's not how it works. We love our children, whatever they do, whatever they become."