FNB SWINDLING CUSTOMERS

I have a loan with FNB that was to be paid in 6 months. After 6 months of regularly paying my account I'm told I'm behind by 1 month and I need to settle the account. I called FNB to find out what's the issue only to realise that my first debit order was deducted then refunded to me without my knowledge. I'm stuck with a loan that's accumulating interest because of someone's mistake on FNBs part and when I call in I get sent from pillar to post with no one willing to take the blame or is able to explain how this happened without notifying the customer about the mistake.... PLEASE HELP!!!