First contact a good local advocate and inform facts and show him documents.
If the deed is registered, mutation or no mutation never matters.
Mutation only is an evidence that such and such is in physical possession.
Mutation neither gives title to property or takes away the rights of property.
It helps in arriving at possession and enjoyment on record.
Some times having such mutation in your father's name helps to claim adverse possession.
Who is in actual possession as on date ? Was the document registered ? Was it obtained in just and proper manner ?