FNB Payment verification

My wife accidently put in an incorrect account number and but the correct recipient name. however this transaction still went through without verifying. Normally a message would pop up to say the account number does not match the said recipient, in this case it did not happen. The amount was a measly amount of R150, which could have been R1500 or R10000. After asking Fnb to reverse the EFT, FNB said the fee to reverse the EFT would be R300. FNB are you going to charge me R300 for a reversal of R150? This is your security breach not my wife's.