Sometimes can be situations when you can't find utility for recovery corrupt autocad files by normal or usual methods. You may refer to following instruments like:
https://knowledge.autodesk.com/support/autocad/troubleshooting/caas/sfdcarticles/sfdcarticles/AutoCAD-File-Corruption.html
http://www.cad-addict.com/2009/07/autocad-use-autosave-files-to-recover.html
https://dwg.recoverytoolbox.com/
