'I was overcharged £7,000 by Student Loans Company'
The Student Loans Company (SLC) has overcharged graduates by £15m in repayments this year, a consumer group has found.
About 57,000 graduates are waiting for refunds, the Which? group discovered, using a freedom of information request.
But the SLC said it could not work out how much had to be repaid until employers filed annual tax returns.
A spokesman told Newsbeat this meant a "time delay" in information getting through the system.
"We are working with HMRC to make sure the information gets through as quickly as possible," he said.
The SLC spokesman said students who chose to make repayments via direct debit would not suffer overpayments, but admitted three per cent had chosen this option.
"There are advantages in paying through the tax system," he added.
"If your salary is reduced for any reason or you stop getting paid, then repayments are reduced or stopped automatically."
Newsbeat spoke to Mark Grieve, a railway worker from Liverpool, who was overcharged by £7,000.
"SLC told me they hadn't received the last two year's Inland Revenue statements, so I got in touch with Inland Revenue and they faxed across copies," he explained.
"When I phoned SLC back they then told me that wasn't adequate and they'd need the past two years of wage slips.
"I managed to somehow find two year's worth, and sent them off but in total it took nine months for them to agree that I'd overpaid.
"Then it took another four months to actually send a cheque out to me," he continued.
"I phoned every week for six months. It was awful, you'd never speak to the same person. I was left very much out of pocket.
"I'd basically say anyone who's thinking of going to uni, don't use the SLC, if you can fund it another way then do."