Bank denying rightful inheritance

My brother passed away 4 years ago and I was named as POD on his savings account when he opened it 30 years ago. Since then the bank has gone through two name changes. With each name change, the savings account number never changed, nor the name of POD beneficiary. When I contacted the bank to inform them of his death and to my claim as beneficiary, they told me that they do not have any one listed on the account as beneficiary. I showed them the savings pass book with my name listed as the POD beneficiary. They would not accept because they said that no one is listed in their records and they want me to go to court to get letters of administration. I have requested that they submit my claim to their legal department so that they can search the archives. My name as the beneficiary is still associated with this savings account number and that neither my name nor the passbook number has changed since the account was opened. The only change happened in the last 30 years was the name of the bank. I want to know what can I do about this? Are my rights being denied?