Debit order dispute can't be reversed

Called yesterday regarding a debit order that went off my account and was adviced to call in 24 hrs so they can do the reversal. Today I called and they told me that they can't reverse the money because the company who debit me put a block on the reversal I mean how is that possible when FNB still has the money and never released the money to the company very disappointed in FNB and there service won't advice any to use this bank they are useless when it comes to reversals its like they support ********* in South Africa. If people ***** your account they won't be able to reverse the transaction nor will they know who the company is. Am so disgusted by there service