Homeloan account

Please I need some who can investigate this account. ********** 390089 I have a home loan account with STDB, ********** 710. I took up a home loan with STDB IN 2015. My query is: I cancelled my assurance policy wit STDB and took an Old mutual one. My argument is before cancelling this policy I used to pay R6 406.32, that is after interest hikes, my initial agreement as per the Home loan agreement was R 5507.54, this amount was also confirmed by the consultant who phoned me to advise me that they have given me the Policy from STDB. After cancelling the policy the repayment amount is still the same. I queried this with STDB and was told that they forgot to add the assurance premiums. My question is, did the system forget to add it? I do not agree with STDB because the system is doing the calculations. I believe that there must be a block or space where the insurance amount must be entered before sending the letter out. The story that they did not include the insurance amount on this agreement is not true. Are they trying to say that the insurance amount must calculated manually, I do not agree with this, because the system is generating the letters with all the information, Please assist