School payroll system Novopay is leaving teachers in crippling debt through mistaken overpayments, with some owing tens of thousands of dollars.
More than 1500 new overpayments have been uncovered this year alone and more than 2000 education workers are in debt they didn't ask for.
Waimarie Stirling has been a teacher for 20 year, and loves her job. She couldn't believe it when she got a letter in the mail telling her she owed Novopay $19,790.
"To get a letter like that in the mail and to say 'you owe this amount of money' - it's shocking!" she told Newshub.
Ms Stirling says Novopay tried to pressure her into repaying immediately.
"I was being victimised for something I had no part in."
Novopay admits the overpayment was their mistake. Ms Stirling was still being paid for extra duties, but it took the payment system took four years to realise.
Ms Stirling says she didn't notice the $4000 a year being drip-fed into her account.
"I just assumed everything was as it should be. Money came in, money went out."
Many teachers told Newshub they feel bullied into paying back more than they can afford.
One Auckland woman who owes $11,000 regrets agreeing to pay back $100 a week.
She says money would have been her only chance to save - now, all her unexpected bills go straight on an interest-incurring credit card.
Recently, Novopay called again and asked her to increase repayments.
More than 2000 education workers owe Novopay because of their overpayments, but only about half are actively repaying.
One worker owes more than $50,000 - and right now, the taxpayer is owed $2.78 million thanks to overpayments.
More mistakes are happening all the time; in 2017 almost 2000 new overpayments were discovered and already this year, more than 1500 have been found.
Teachers' union NZEI says it gets a constant stream of phone calls from teachers stressed about Novopay.
"We would regard the level of problems as still excessive," said general secretary Paul Gaulter.
The system is managed by Government-owned company Education Payroll.
It took over from private firm Talent2 in 2014, after tens of thousands of teachers were underpaid and overpaid.
Newshub wanted to ask it about the ongoing mistakes, but both it and the Education Ministry refused.
In a statement, the CEO said Ms Stirling was treated with "respect" and has apologised to her.
It only uses debt collectors a "last resort", and for debts of more than $2000 it initially tries to get people to repay in one year.
Employment lawyer Bridget Smith says in the private sphere, workers who didn't know they were being overpaid often negotiate discounts and teachers should too.
"If the employee can say 'I didn't know, I shouldn't reasonably have known and I've changed my circumstances', then they may have a really strong argument."
In hardship, a court could also wipe the debt.
Ms Stirling says she can't afford to make repayments at the moment, and wants teachers to rigorously check every payslip so they don't end up like her.