Wesbank cannot do simple calculations

Extremely bad at maths. I requested that my car repayment loan date be changed on the 20th of August which in essence would be effective the 25th of August and this change was done on the FNB app and it notified me I would be contacted by someone from Wesbank shortly. I only received a call on the 2nd of September which was the first problem. The reason I requested my repayment date be changed was due to a change in the salary date payment which changed from the 25th to the last day of the month, so I requested my repayment date be changed to the 1st day of the month. When I spoke to the gentleman on the phone when they finally called, I specifically asked if the repayment amount would change and he told me it would remain the same, only the payment date would be changed which I was happy with. When the debi-check order appeared on my FNB app, the amount shown was R69 higher than it should have been which makes absolutely no sense as the service fee is already included in my monthly payment so having a of R138 makes no sense, I rejected the debit order then. The documents emailed to me today also show the service fee of R138 which is way above the legal limit, as well as the changed date and amount even though I rejected the debi-order. Please may you rectify this ASAP and change it back to the original monthly payment I should actually be paying especially given that I specifically asked the question and was assured the payment would remain the same, as well as change the date to the 1st of the Month. Not sure how Wesbank does their calculations, but clearly a terrible mistake was made with the calculations.