What can i do to get a lien holder to sign off title?

I live in Michigan and I recently filed bankruptcy. I had a secured loan which II used a vehicle for collateral. I contacted the creditor to surrender the car but they did not want it. This debt was discharged through my bankruptcy. My attorney told me since they refused the car I could donate the vehicle to a charity which I did. My problem now is the company is refusing to release the lien on th