Nedbank Home loans *********** personnel

Nedbank changed my debit order for my home loan several times over the past year. I did query it a few times. The problem is that they give me different answers every time. On 04/08/15 I read an email from Mr. Sugrendi Mohanlall stating that the amount was less because of extra payments that was made into my account. He stated that my debit order was not fixed and that extra payment or withdrawals would influence the amount debited every month. On 01/09/2015 Nedbank debited R 3022-42 more from my account....??? Do not understand this as I paid extra money into the account and therefor the amount should be less. My personal banker did send a query to home loans department. Nadia Theron rep**** and stated that my debit order amount was fixed?? The question was simple and straight forward. I wanted to know why the amount was increased. I did reply to her and received an email back stating that I am not allowed to send email to her personal mailbox and that I need to refer the matter to NCC and log a case. Not sure why a Nedbank business email is regarded as personal. Why must I log a case to get answers from them. Their actions are suspicious and ***********!!! POOR service Nadia!!!!!