No solution for opening a bank account for a deceased person

my mother is trying to open a bank account in order to receive a claim on my deceased father's estate. amongst the other requested documents, she has a certificate of appointment which FNB says they cannot accept as they require a letter of authority instead. now the issue with this is that pre-2005, certificates of appointments were issued and not letter of authorities, but the bank wont accept this. we have had to travel to another province to visit the magistrate that issued the certificate of appointment back in 2002 to ask for a letter of authority and they said they would not be able to convert this document into a letter of authority . a certificate of appointment should still be valid for all issuances that took place before 2005. this is a frustrating process for my mother and we no longer know what to do. what dies the bank suggest that we do????????