It is a grim place to die: a bunk bed in a filthy, crowded room, deep within Qatar’s largest labour camp, thousands of miles from home.

As Rupchandra Rumba lay there in the early hours of 23 June, his friends heard him struggle for breath.

“Those who were sleeping next to him that night said he twice made a strange noise as if someone was choking him. Then he fell unconscious,” says a co-worker. “There was a sense of fear and panic after he died. We were afraid to sleep in that room.”

Rumba, a labourer from Nepal, had been working as a scaffolder for two months at the Education City football stadium, a new 40,000-seat arena set to host a World Cup quarter-final in three years’ time. He was employed by a labour supply company – a firm that farms out its workers wherever they are needed.

Like hundreds of other young migrant workers who die in Qatar every year, his sudden and unexplained death was attributed to “acute cardio respiratory failure due to natural cause[s]”.

But Rumba was just 24. His friends and wife say he was perfectly healthy. He didn’t drink and only occasionally smoked – he could not afford more than a couple of cigarettes a day.

Last year nine World Cup stadium workers died of “natural causes”, which the World Cup organisers call, “non-work related deaths”.

Deaths from natural causes are never investigated. Yet a Guardian investigation has found that migrant workers like Rumba can be exposed to hours of extreme heat stress every day for months at a time over the summer. Cardiologists now say that heat stress is the direct cause of the high numbers of deaths attributed to cardiovascular problems in Qatar.

In its most recent report on worker welfare, the Supreme Committee organising the World Cup boasts of a “core mission to ensure a sustained culture of health, safety and welfare”.

But Rumba’s death shows how far they have to go. Cardiologists say that heat stress fatalities can be avoided if the signs of heat stress are recognised and people get access to healthcare quickly. Yet Rumba’s workmates say they have not even been issued with a mandatory health card by their employer, which would entitle them to low-cost or free healthcare.

Rumba’s wife, Nirmala Pakrin, 26, worries how she will support her son. Photograph: Pete Pattisson

“If someone is sick, the camp bosses don’t let us go to hospital. They just give us a Panadol,” says another one of Rumba’s co-workers.

Far from the glistening towers of Doha, Rumba’s wife, Nirmala Pakrin, lives with their six-year-old son, Niraj, in a room on the outskirts of Kathmandu.

Pakrin spoke to her husband regularly. “He told me he was working at the stadium. He said the work was not difficult, but he complained about the pay. He said he had not got his salary for three months. He said the camp boss used to swear at them and beat them sometimes,” she says, swiping through photos of her husband on her phone.

Then she received a call from a number she did not recognise. It was Rumba’s camp boss, calling to tell her that her husband had died.

His death has left her shocked and confused. “I don’t remember him ever complaining about his health. I can’t remember the last time he was unwell. He complained about the heat; how hot it was, how much he would sweat, but there was no hint that he was sick,” she says.

Pakrin has been left with no husband, no income and no compensation from Qatar. The only money she has received from one of the richest countries in the world has come from Rumba’s impoverished workmates, who all chipped in to send her 67,000 rupees (£470).

“I called the company boss and asked him for money. He said … since [Rumba died] in the camp he was not eligible for compensation. All they could do was send his body back,” says Pakrin.

Last year the Guardian revealed two cases where the Nepalis working on World Cup stadiums had died, and five months on, their families had not yet received compensation. The workers’ employers have since made these payments.

Pakrin now says she doesn’t know what she will do or how to provide for their son, Niraj. “He says his dad promised to bring chocolates when he came home,” says Pakrin. “He keeps asking, ‘Where’s my dad?’”

The Qatar Supreme Committee confirmed Rumba’s death but said that the sub-contractor employing Rumba at the time was not pre-approved to mobilise on the World Cup stadium site. As a result Rumba had not received a comprehensive medical screening. It is launching a full investigation into how this happened.