Refusing to close and paid up account

I had a loan from them that I maintained impeccably for 4 years, I even made an additional R20k on 19 January 2017 to settle faster. The last debit order went of on 26 December 2017, and on the 29th of December I was promised by the customer service that the account will be closed. On 11 January 2018 I received an statement indicating that they now ow me just over R300.00 but it still states that there will be a full deduction on 26 January 2018. Obviously the account was not closed as promised. This morning i called their customer service where i was put on hold for 20 minutes before i put down. I then called back and this time i was told the the settlement amount is just over 6k, which are completely incorrect and then I was put on hold for another 30 minutes without anyone coming back on line. The third time i had to use threats of reporting to the ombudsman to get to speak to a supervisor. I was then told hat they cannot close my account , as i need to provide proof of payment , A PAYMENT MADE A YEAR AGO!!!!!!!. When i questioned this I was told that this is the process., even though my monthly statement has reflected this payment , every month for 12 months, and that they cannot close my PAID-UP account if I don't provide this to them. I tried to explain that I had done an internal account transfer on the FNB app , from my cheque account to the personal loan account and that all that shows on the statement is the description and the amount , no account numbers and that I am not giving them my bank statement as their own statement shows that the payment was ****, it was capitalised and deducted of my outstanding balance.

Why am i being penalised for paying additional monies int a loan, why do i have to proof that I made a payment when it has been on your own statements for 12 months and why are your company refusing to close and account that has been paid up for nearly 30 days.