I'm payee on checking acct and custodian. How can I get a freeze lifted to close the account?

My mother was killed 3/9/15 and I was her Aid and Attendant paid by Veteran Admin and I was on the bank acct as the payee and she was noted as dementia so she could not do anything with the acct. The bank froze the acct and will not let me have the money, said I have to provide the notice of successor. I am the custodian of the acct. How can I get this lifted to close the acct?