Unable to get title for a used car

Location: MN

My husband is a automotive technician and he bought a car off a customer for cheap to fix up.

When we went to get the new title, we were told this 17 year old car still had a lein on it.

We contacted the prior owners who gave us documents from a loan they got with this car as collateral, but the DMV is saying we need the lien release from the original loan which weve now been unable to get. The DMV has essentially said we are out of luck, and they won't title it and the prior owners don't have documents and are unwilling to assist further.

Unfortunately my husband has already fixed the car, so although it's a small amount were out about $700 with repairs and purchase price for a car we can't drive or resell.

Do we have any other options?

Thank you!