When you read the thread that SeekingKnowledge linked to, pay particular attention to the excerpt from the Green Book that Ken posted.
You have an account opened for an entity without evidence of authority of the person who is acting on behalf of the entity. That's sufficient cause to suspend use of the account pending the outcome of your fraud investigation. This includes cancelling the debit card and returning any ACH payments that are in the signer's name (I suspect that all of them are in the signer's name). During your investigation, you'll want to contact the leadership of the church to advise them of the existence of the account- they have a stake in this matter, too.
With respect to the federal benefits deposit, your only logical choice is to return the deposit to the Treasury, since you do not have an account in the beneficiary's name to credit the funds to.