For the past week, Khandhar Kaliph's hands have trembled whenever his phone has rung.

He nervously greeted his daughter, who had been kidnapped when the Islamic State (Isis) overran the Yazidi city of Sinjar. There was a minute of silence, before he broke down sobbing.

"She said she is going to be sold as a slave this afternoon, for $10," Kaliph said, his tears dropping into the brown dust. "What can a father say to that. How can I help? We all feel so useless."

Kaliph's daughter, who he did not want to name, had access to a group phone passed around between other girls imprisoned by the Islamic State in Bardoush prison in central Mosul.

All face the imminent prospect of being married off. Or worse, being used by the jihadis as a sex slave.

"The world needs to know that is where our women are, where they are being enslaved, young and old alike," he said, sitting in the dirt outside a building site near the Iraqi Kurdish city of Dohuk that he and some 70 other Yazidis are now using as shelter.

Dohuk and the strip of land to the Fishkhabour crossing into Syria are now teeming with Yazidis, who have escaped in the past 48 hours from Mount Sinjar in northern Iraq, where they had been besieged by Isis. Nearly all the Yazidis the Guardian met offered stories of women and girls being kidnapped, or of men being killed in the brutal rampage that has shattered centuries of coexistence in Iraq's north-west.

"We didn't know what hit us," said a man who joined the conversation. "We were asleep one minute, and running for our lives the next."

Some Yazidi men say they had phoned their daughter or wife's phone number only to be told tersely by strange male voices not to call again.

"It's more than our heritage," said Wadhah Jowla, another father squatting helplessly in the soil. "It's our heart and soul. My daughter means more than anything to me. She is not in Bardoush prison, but we are sure she is in Tel Afar [a nearby town]."

Of all the minorities ousted by the Isis advance, the Yazidis continue to pay the biggest price. Their self-contained existence on the Ninevah plains, where they had long been in the cross-hairs of jihadis, has been shattered in a bloodlust that has also sent the area's Christians, Shabbak Shias and Turkmen fleeing to Irbil. A large number of those who fled Sinjar climbed the nearby mountain range, where many remain trapped.

The jihadis regard the Yazidis, who practice a Zoroastrarian religion, as devil worshippers and have been more ruthless in their pursuit of them than they have against other minorities.

Those who have reached the Kurdish north to tell their stories say they are never going back. "It is finished," said Kaliph. "There is no Iraq. There is no past either. It is a scorched earth.

"But don't forget about those who have been left behind."

In a hospital in Dohuk, five elderly Yazidi men were recovering from their arduous journey down the mountain's northern face, escorted by Kurdish rebels first across the Syrian border, then into Iraqi Kurdistan.

"I've never done anything more difficult," said Salam Hadid, from his hospital bed. "They were trying to kill us the whole way," he said of the jihadis.

"People were so exhausted that they were gradually shedding their belongings as they walked, clothes, valuables – anything to make their load easier."

A second Yazidi man, Issa Mouallem, said the sound of jet planes and blasts roared through the air throughout their escape. "We were lucky," he said. "We could get out. But some of those trapped have no way out at all. And many of them are incapacitated. They are old, or they are vulnerable."

In Dohuk, and in the border town of Zakho, Yazidi families appear to have taken refuge in every public space and unfinished building. Families were hanging out washing in half-completed homes, or setting up plastic tents outside petrol stations and on grass verges.

"Some of the kind-hearted people gave us food," said Kaliph. "We are depending on their goodwill to survive."

Kurdish and US officials suggest as many as 20,000 people may still be on the southern side of the mountain, all in desperate need of aid. Many are too incapacitated to make it to points where food and water has been air-dropped, the main site being a disused airfield at the top of the mountain range.