FNB unprofessional in handling estates

FNB is in charge of my grandparent's estate. My grandfather passed away in 2009. My grandmother past away last year. In 2009 everything in the estate was shown and accounted for. Its taken over 6 months now for FNB to give documentation and evidence on where 60% of the estate has vanished. It's a large amount that is missing. No one from FNB is coming forward and all we get is they can't find it.