FNB, how can we not help you?

Please explain how I have a signed contract and debit order authorization for a set amount from Home Loans and FNB debits my account with another amount? Its four months running, and I am still trying to sort out this matter. I get told it's a system error, yet no resolution in place other than me filling in another form, requesting FNB to reduce my monthly payment, like I made the mistake. No mention of being reinbursed, nothing. Sign the form or else... So maybe the Ombudsman can help because FNB surely cannot