After Nate suffered his 2nd stroke in 2008, he moved in to a CareMeridian treatment facility in Orange County ... a place dedicated to rehabbing and caring for patients who suffer from catastrophic injuries.

In legal papers obtained by TMZ, CareMeridian claimed the singer received more than $290,000 in medical treatment from 2008 until 2010 ... and one of Nate's managers, David Michery, personally guaranteed the facility would get paid.

But according to the lawsuit, the check never came ... even after Nate died in 2011.

Now, the court has entered a default judgment against Nate's camp ... including Michery ... ordering them to shell out $293,512.52.

Nate was a TITAN in the music industry and made millions of dollars during his career ... so it's unclear why no one's paid up. - more on this story

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