Do you have any evidence of bad mouthing?
Is there any evidence in writing; say BGV?
Did you ask for a copy? Do you have a copy?
Did you lose any employment due to it?
In case it is all verbal would anyone that is involved/concerned in last/prospective employment, agree to be your unshakable evidence?
Probably not!
So how would you establish?
In case you can establish go ahead and press for damages, if you want.
Or have you written to last employer (under proper acknowledgment with a copy to you) that they have posting adverse comments against you that lead to losing employment by you?