Post retiral dues are not bounty of the State Govt but the valuable rights of your father.
If no Department Inquiry is pending against your father, there was no occasion for the Home Department to withold the post retiral dues of your father.
The State Govt' act of withholding the post retiral dues of your father, is infringing his fundamental rights as available to him under Articles 14, 19 and 21.
Immediately approach the High Court so that these dues are released forthwith.