bad treatment

I have a personal loan with FNB and in August I went to fnb in Sandton and a lady assisted me with my documents from work stating that from the 1st of September I'll be on Maternity leave so that they can reduce my installment and she spoke with someone from loans department. Then on the 27th I received an email from the loans department stating that I'll be paying R300 and something. Then on 23rd of September I got paid my 40% salary and R1002.92 was debited from my account and on friday the 25th I went to the FNB branch in Alexandra and the person who assisted me called the collections department and I spoke with Ntombi she's the team leader and I explained everything to her and we even sent the letter. that was sent to me regarding the payment arrangement but she said I didn't agree to the terms and conditions of the arrangement and I told her that the email that was sent to me doesn't specify where I should reply to. And she said there's nothing she can do for coz I didn't do what I was supposed to do. If that's how fnb treats their costomers its not fair Coz I needed that money back I have kids that needs to eat and I need to pay their school fees, I'm disappointed