password to unlock filevault vol not accepted

You won't get anywhere unless you provide the FileVault password.

Excerpted from Use FileVault to encrypt the startup disk on your Mac - Apple Support:

If you forget your account password or it doesn't work, you might be able to reset your password.

When you first encrypted the original drive with FileVault2 it would have given you the choice of storing a 'recovery key' either in your iCloud account, or it would have displayed this recovery key on your screen for you to note down and store in a safe place.

The purpose of this recovery key was so that if you ever forgot the correct password an alternative password i.e. the 'recovery key' could be used instead.

See this article for what the original process would have looked like and in particular the section about the recovery key.

https://support.blakeschool.org/hc/en-us/articles/231784808-Enable-FileVault-Enc ryption-on-Your-Mac

If you have forgotten all the valid passwords - there would be one per authorised user, and you have also lost the recovery key then you are not going to be able to access it. The whole point of secure encryption as used in FileVault2 is to prevent people from being able to break in to it and access the contents.

Note: Apple will not be able to unlock it for you either.

Do you have a backup? You should always have backups. Of course if you are using FileVault2 then your backup should also be encrypted although this could be with a different password.