In that case, don't read too much about how ACH actually works. You are supposed to obtain authorization first, but this is not generally verified at the time

In that case, don't read too much about how ACH actually works. You are supposed to obtain authorization first, but this is not generally verified at the time of the transaction (some accounts do white list specific accounts for outgoing ACH transfers). People can pull money out of your account with just your account and routing numbers. The only way to initial an ACH chargeback is to attest under penalty of perjury that you did not authorize the transfer. (Not receiving the product / fulfilling the terms of the contract is not a valid chargeback reason for ACH). So if you had indeed authorized the transfer (as maroperaza stipulates) then your only recourse is to sue them in court.