Incorret Billing

I took a loan from Nedbank in October 2011 at interest rate of 22%. The instalment was R1595. I defaulted for 2 months over the period of the loan and paid all the arrears of R4900 in September 2015. In October I requested for a statement and the balance of R3129 was reflected on the statement. I received an email confirming that I will be paying the last instalment in December. In November I paid the instalment of R1595 and surprisingly I was told that the balance is R1910. I lodged the complaint with Nedbank and they told me that the balance includes other fees however they could not explain what the fees relates to. On the 21 December I requested for a settlement amount, the letter reflected the settlement balance as R2008.64, instalment as R1402.36 and balance as R1973.10. A statement was also sent to me on the same day it reflected the instalment as R1595.52 and the outstanding balance as R1861.81. There is a discrepancy with the billing as it does not tie up and I have raised this issue with Nedbank however they refused to address the issue.Although I have paid the settlement to avoid further fees charged, I want them to reimburse me as I am fully convinced that their billing