Ram Kumar Mahara says he was not paid for 12-hour shifts on sites building the infrastructure for 2022 World Cup

If things had gone well, Ram Kumar Mahara would be working on a Qatari building site, earning around £120 a month helping the country to erect the infrastructure that will enable it to host the football World Cup in 2022.

But things didn't go well.

First there was the pay. Ram Kumar says there wasn't any. Then there were the conditions – 12-hour shifts, a shortage of food and finally, after a complaint to the manager, summary removal from the labour camp. It was so distressing that the 27-year-old Nepali lost his hair. After weeks in legal limbo at the Nepali embassy in Doha, he finally made it home. The nightmare was over, but a new one was just beginning.

"I spent six months in Qatar but did not receive a single rupee," he said from a remote village in Nepal, where he has found piecemeal work threshing cattle fodder.

"I was reluctant to come back home as I didn't earn any money ... When I got home my wife was weeping and even I did not feel good. I still feel very guilty. I have not done anything since I got back," he said. "I just sit at home looking after my children. I came here for 10 days of work ... but it does not pay much."

Ram Kumar was one of the Nepali workers who spoke to the Guardian for an investigation that exposed systematic exploitation of Nepalese migrant workers in Qatar's booming construction industry, including on a site directly linked to the 2022 World Cup.

The investigation found high levels of fatalities (44 in eight weeks over the summer), terrible living conditions and labour practices that in effect enslaved the migrant workers, depriving them of pay, permits and freedom to move around.

He paid a local agent in his village 120,000 rupees (about £775) to go to Qatar, far in excess of the legal limit stipulated by the government. The only way he could afford this was to borrow the money at an annual interest rate of 60%, but because he was unable to send any money home, his debt quickly ballooned to 500,000 rupees.

"When I was abroad, my wife took out more loans as my children were ill, so our debt grew to this huge amount," explained Ram Kumar. "The only way I can pay it off is by going back abroad."

In Qatar, Ram Kumar says he sometimes went 24 hours without food – "12 hours' work and then no food all night".

"When I complained, my manager assaulted me, kicked me out of the labour camp I lived in and refused to pay me anything. I had to beg for food from other workers."

He rapidly found himself trapped, without a salary or the exit permit he needed to leave Qatar. Eventually, with the help of the Nepali embassy, he was able to return home, but he had to leave his salary, and his dignity, behind.

Now back home in Nepal, Ram Kumar may have escaped Qatar, but he is still bound by the debt he took on in order to pay Nepali recruitment agents for his job there. His attempts to get his money back have proved fruitless. "When I got home I asked the local agent to return my money, as well as my unpaid salary," he said. "He told me he would pay me back … but he has not given me anything so far."

Despite being deceived by his local agent, Ram Kumar places the blame for his ordeal squarely with the Kathmandu-based agency, Marvelous Employment Nepal. There are more than 700 registered recruitment agencies, known as manpower companies, in the capital, Kathmandu. They rely on a network of thousands of unregulated local agents, who send workers to them from across the country, often for extortionate fees.

"It is the manpower company that cheated me. I called them [from Qatar] after I did not receive my salary, but they just consoled me every time saying they would talk to the company," he said.

Marvelous Employment Nepal denied any wrongdoing. "We sent the return air ticket to bring Ram Kumar back from Qatar and we are no longer sending workers to that company. We offered to help him get a job in another country," said Kumar Gauli, the company's marketing director. "We are ready to negotiate with Ram Kumar and help him as much as we can. We are willing to return what he paid to us."

Marvelous Employment Nepal disputed Ram Kumar's claim that he did not receive any salary in Qatar.

"The recruitment agency has basically tried to buy off Ram Kumar by offering him another job instead of paying him the full compensation he deserves," said Samar Thapa, of the General Federation of Nepalese Trade Unions. "We have to encourage the workers to punish the agencies or they will never change their behaviour."

Until then, Ram Kumar and his wife, Hira Devi, have little choice. "My husband should go abroad again to work … so that we can pay back our loans and manage our daily expenses," she said. "I am worried as I have small children, two daughters and a son, to look after. I don't even have any land or a home and we are in huge debt."

"If people asked for my advice, I would say Qatar is not a good place, so don't go to Qatar. I had a very hard time there," said Ram Kumar. "I would tell people to go to other countries, but I would not recommend anyone to go to Qatar."