Suspect interest calculation on bond

FNB Housing Finance is ignoring my query... On 2017/08/08 I requested FNB Housing finance to provide me with a breakdown of interest calculation because according to my bond statement the amount of interest I was charged in July 2017 is more than the interest charged in Feb 2017, even though the difference between these months balances is over R10079, and the interest rate is the same. This prompted me to compare interest I was charged in 2011 to the one I am currently charged (NB. Difference in balance is over R100000...) I found out that I am still charged the same amount of interest. PLEASE NOTE: I am aware that interest is charged daily on the outstanding bond amount. As a client of FNB, I believe that I am entitled to have the formula that FNB Housing Finance is applying to my bond interest calculation disclosed to me so that I may be free to apply it myself and to verify the accuracy of the charges....