Over payment not being refunded

Most pathetic service ever. My FNB loan account was handed over to their company. I received an sms on a discount for my account. They were quick to send me a settlement letter, kept on harassing me with reminders for payment. I made 2x payments into the account, when I called to ask for a refund of the one payment I was asked to submit both proof of payments, screen shots of the sms FNB sent to confirm both payments as well as my bank statement. I never got a reply after that. I called a week later to query my refund and apparently this is my problem.