When the letter landed on Crina Petrariu's doormat at the home she shares with her husband and young son in Hull, she assumed there had been a mistake. The short, official note stated that the second-year chemistry student's financial support had been frozen – and that she now owed the government £3,500.

"It was a shock but I didn't really think it could be right," said the 34-year-old Romanian in a break between studying and looking after her six-year-old son, Rares. "I called the student finance people and they said it was a new law and that the government had said to stop all finance to Romanians and Bulgarians."

Two months later, despite repeated phone calls and sending off a parcel of bank statements to prove she has lived in Britain for more than the three years qualifying her for student maintenance support, Petrariu, a student at Hull University, says she still has not had a penny of her allowance or tuition fee support.

"Every time when you call them, they say they are still checking. 'We don't have an answer for you yet.' But it has been more than three months now. It is getting very hard."

Petrariu, who has lived in Britain for five years and whose husband has just got a job as a secondary school maths teacher, was one of about 7,500 Romanian and Bulgarian students who had their financial support – fees and maintenance allowance – frozen without warning in November last year.

The government said it suspended the grants and loans after noticing an upsurge in the number of students from the two countries applying for maintenance support. Officials asked them for fresh proof they had been resident in the UK for the qualifying three years.

The move coincided with increasingly hostile rhetoric about the anticipated influx of "beggars and benefits cheats" from the two countries when working restrictions to Britain were lifted on 1 January. And some students fear they have been caught up in the government's efforts to appear tough on immigration.

Andrei Stan, a student at Sheffield University, is the co-ordinator for the UK branch of the League of Romanian Students Abroad. He said some Romanians had been forced to abandon their studies as the money dried up – and many more were sceptical about the government's motives.

"The timing of this announcement and the very precise targeting – that only students from these two countries, out of all other EU member states, were initially involved – leads to the suspicion that there may have been a party political motivation for this initiative, with legitimate Romanian and Bulgarian students paying the price."

David Willets, the universities minister, announced the initial crackdown in a written statement in November. This was subsequently extended to cover other EU students at private colleges who claimed maintenance allowance, but it is only Romanians and Bulgarians at both private and public universities who have been affected.

Ion Jinga, Romania's ambassador to the UK, says he has received several letters from students who have been caught up in the clampdown, some of whom have been in Britain for 10 years. One 18-year-old got in touch to say she had received a letter just after Christmas telling her she had to repay £9,000 in 10 days or prove she had been in the country for three years by sending utility bills, council tax or bank statements in her name.

"The problem is that when you are 15 you do not put these things in your name," said Jinga. "So she sent them an official letter from the UK Border Agency proving she has been a resident in the UK since 2010, as well as diplomas from her UK secondary school and college. But still their answer was negative, and now she does not know what to do."

Jinga said he was 100% supportive of any legitimate measure to stop fraud, but he was concerned that Romanians and Bulgarians had been targeted, adding that this could lead to discrimination.

"These students appear to have become caught up in this political and media storm around immigration, and they did not want to be caught up in it, and they did not ask to be involved," he said.

The government has so far failed to give any specific details of the increase in Romanian and Bulgarian students applying for maintenance allowance in England. A spokesperson for the Department of Business Innovation and Skills [BIS] said it would be providing a breakdown in the next few weeks, adding that proof of entry requirements had been toughened up for all EU students applying for maintenance allowance. "We identified that there had been a significant increase in the number of Bulgarian and Romanian students applying for full student support in England this year … We have asked each of these students to supply additional information to support their applications for maintenance, before any further public funding is made available to them or to their institutions."

Andrew McGettigan, an expert in higher education, said the problem had arisen because the Student Loans Company [SLC] has no appropriate process to deal with young Romanians and Bulgarians who have moved to Britain with their professional parents in the past 10 years and who are now heading to university.

"This is a problem of poor information management between different branches of government," said McGettigan, author of The Great University Gamble: Money, Markets and the Future of Higher Education. "Officials at BIS and SLC saw the figures claiming maintenance support from Romanian and Bulgarian applicants and did not believe that so many people had been here legitimately for three years. They may have stopped some fraud, but this issue is not confined to Romanian and Bulgarian students, and many of these young people who are here totally legitimately have had their studies jeopardised."

A spokesperson for the Student Loans Company said that as soon as it received proof from students that they had lived in Britain for three years their funding would be reinstated.

But as the debate about what has happened and why Romanians and Bulgarians have been singled out continues, time is running out for students like Petrariu. "I am worried now because it is getting very difficult. I have a child and we are struggling with money. Our credit cards are empty ... Please don't mess up my life with your political games. Yes, I know the politicians will probably win lots of votes, but it is affecting our lives and that doesn't feel fair."