Money being taken away from FNB account without authority

FNB closed our account without informing us that our account would be closed/has been closed and taken the money away. When I tried to claim the money back from FNB, I was told that the authority that my mum gave me to manage her account has fallen away MERELY BECAUSE FNB HAS CLOSED THE ACCOUNT, WHILE MY MUM DID NOT/ HAS NOT WITHDRAWN THE AUTHORITY!

Now, FNB insists that my mum must come to South Africa and claim the money herself and unwilling to reinstate the account and transfer the money back to her account.

Our concerns are that her money being taken away without being informed and unwilling to reinstate the account!