Standard Bank lying about signed agreement on Homeloan

Standard bank decided to increase my interest on my home loan for no valid reason.

I was on debt review but off debt review from Jan 2017. I got a bond extension and signed a new agreement with interest rates specified (plus or minus prime/applicable rate).

Standard bank now claims that because i was on debt review now suddenly i get a "risk rate".

How can i get a risk rate more than a year after being off of debt review AND in the mean time granted a bond extension while NOT being on debt review ?

They claim it is a concession rate, however now here in the contract signed is mention of any concession or review of rates unless the applicable/prime rate changes (which is normal)

The lady that called me tried to convince me that a concession is inferred in the contract however when pushed on the matter she cant explain how something NOT written is written . I have never missed or made a late payment on the bond, as a matter of fact i have frequently paid MORE.

I was promised feedback by 17:00 on the 5th of April 2017 yet no answer as yet.