Monthly instalment increased

I went through a debt review process two years back.The debt counsellors negociated my monthly instalment to reduce by less than R150,00 per month.When I exited debt review process i was told that my monthly instalment will remain the same<br> <br> In May 2015 i received a call from Standard bank home loan telling me that my home loan account was granted a subsity and this resulted in my being on arrears.I asked of how much i needed to pay to bring my account up to date and i was told that I needed to pay R2100 and my account will be up to date of which I did<br> <br> To my surprise Standard bank debited R2453,00 instead of R2300.When i called home loans to find out why my monthly instalment increased i was told that the money debited from my account was still not my full monthly instalment and was told that my monthly instalment is R4029,28 and i was shocked.They said this was due to interest debit increased<br> <br> I need to know how my instalment moved from R2300 to R4029.28 and how is it possible to increase it by almost R1500