While their employment initially complied with the Minimum Wage Act, that changed as the employees began working "excessive hours" which meant they ended up being paid less than minimum wage.
However, they did have free accommodation and could get food free from the stores they worked at.
The decision noted the three workers had suffered substantial financial losses, depression, stress and anxiety.
They also lost money in the form of wages and holiday pay which has since been repaid.
Labour inspectorate retail sector lead Loua Ward said the workers originally came to New Zealand on student visas and upon completion of their studies, secured work visas to allow them to work as shop assistants.
"The employees were underpaid and overworked. In addition to undertaking shop assistant tasks, the workers looked after their employers' children, washed their cars, and cleaned their houses."
Prabh Ltd, Kaur and Singh will also be placed on the stand down list for two years and be prevented from hiring migrant workers for that time.
The case follows an investigation by the Labour Inspectorate, first heard at the Employment Relations Authority, before new employment legislation was introduced to address serious breaches of minimum employment entitlements, which allowed it to be moved to the Employment Court.
The court ruled the treatment of the three employees was such a persistent breach over a long period of time, that it could not have been considered unintentional.
The breaches also included failure to keep wage records and evidence of retrospective creation of employment agreements, going back to 2014.
Prabh Ltd had received previous reminders from the Labour Inspectorate of its obligations to provide minimum wages, holidays and holiday pay, following a complaint made by a former staff member.
"These two employers took unfair advantage of this situation, and the Judge agreed they had no intention of paying them what they were legally owed," Ward said.
She said migrant workers were a vulnerable section of the work force as they could be less likely to be aware of their rights as workers.
"Addressing this exploitation is a priority for the inspectorate and we continue to work with Immigration New Zealand and other government agencies to combat migrant exploitation."
The Employment Court decision stated the circumstances of the breaches were "heinous" and the employees were treated in an "appalling way".
"The defendants' conduct was a cynical and concerted action to take advantage of young persons trying to enhance their education in New Zealand," it noted.
"This case involved serious and persistent breaches over a lengthy period of employment."
MBIE encourages anyone concerned about their employment situation, or the situation of someone they know, to call 0800 20 90 20 where they can report their concerns in a safe environment.