Fnb suspicious *****

Good day I'm very upset..my husband have 2 accounts with FNB, the one he opened when he retired last year. So he saved a certain amount of money and no one can touch that money. All of a sudden last week Thursday we saw a huge amount of R9000 disappeared out of his account. He went to them to ask what happened they told him that money was transferred to his aspire account. That they can do nothing about it which is not true. No one can touch that money because it's an investment...now our question is what can we do about this matter or must we take it to the police station and open a case for *****? Because if it was transferred to the other account then that amount was supposed to be more which is not and the statement shows duplicated amounts out of the account...