Dissatisfaction about FNB Bank service

My house is financed by FNB since 2016, i have been paying extra on my monthly installments and i found out that I have more than R30 000 aside from the money i have been paying. They promised to pay that extra money back into my account but until today i have not been refunded. That was months ago. Recently i wanted to settle my remaining balance with the bond but FNB is making it impossible for me to do so. I don't know what else to do. Please help me