Michael Mendez's son Nathyis has autism and an attention disorder.  He relies on two therapists who have helped him start to progress in school.

"He loves them. He loves to be with them. He talks about them all the time," Michael Mendez said.

Both therapists are contract employees and rely on the Education Department to reimburse them each month for their work. But they're now owed several months of pay, and Michael is scared how this might impact his son.

"These providers, they have families to take care of and at some point, if they're not being paid, they're going to have to go somewhere where they are getting paid and I potentially will lose the services," Mendez said.

The Department of Education acknowledges that there is, once again, a backlog of overdue payments for special education providers.

In October, NY1 exposed how the office responsible for paying special education providers had amassed a staggering stockpile of unpaid invoices, many going back five, six, seven months.

Therapists described defaulting on their mortgage, student loan and car payments as they waited to be paid for their work. Mayor de Blasio and Chancellor Richard Carranza called the situation unacceptable and vowed to fix it.

Three weeks later, the city said it was all caught up on 7,000 overdue payments.

But now, the delays are back. Advocates for Children of New York says the volume of complaints increased significantly again this month.

"These are payments which the Department of Education has been ordered to pay by an administrative hearing officer and they're still not paying them," said Rebecca Shore of Advocates for Children.

The Department of Education says the number of special education services it pays for has more than doubled since 2015.

A spokeswoman says it is currently behind on 350 service orders - some of which could include several months of backpay. She says this month new permanent staff was put in place to get payments out on time, and they are working on long-term solutions.

For families like the Mendez's, it's been very concerning.

"It's not easy to find the right team of people to provide you services and when you do, it's very stressful to think we could lose that," Mr. Mendez said.