How to get a release of lein when the company is no longer in business

My parents are in the process of selling their house. During the title search it was found that there was a lein from 2001 that was never discharged. In doing research it was when the mortgage was bought and sold to another company and the seller never filed that they were paid by the new. Since that time the mortgage passed through several other lenders through selling without issue. Now they find out the mortgage company that never filed the paperwork is not in business anymore. They can't get anyone to help. It doesn't make sense that this has passed through several other companies and nobody has raised this issue (obviously they have been paid by the next company!). Any help would be great. State is New Jersey.