Why they always telling me to pay arrears of which I don't know where are they coming from. And my installment is high is not lowered as they promised.

Last month fnb consultant told me that I'm in arrears. Of which I need to pay. They sent me an email confirming that I need to settled tht amount of R19400.i did pay the following day. After sending them the proof of payment. The guy called Zaheer Ebrahim said I'm in arears of R8600.when I complained about why they told me to pay 19400 and the following week they told me about other money no one helped me. The even said after paying that R19400 they will lowered my installment. Now they treat me like stupid. Now they are frustrating me where is this arrears coming from no one game me an answer. I did pay that R8600 of which I don't know is for what I'm scared cause they will black list my name. As a client of FNB their treated is not good at all