Increased installment without any explanation

I am so frustrated with nedbank, firstly I tried to communicate with them via their email contact, and they were of no help. After the back and forth I was asked to call the call center which I did. Another nightmare, from getting transfered to different people, some just keep quiet after I tell them my issue, and eventually hang up on me after seeing that I'm still holding. Then I would call back, and explain myself all over again, get transfered to another consultant n they just keep quiet after I tell them my issue. All I wanted to know is why is there an increase in my installment just after my bond got registered.