Breach of contract

I received a letter stating that my step up account will increase as from 01-05-2015, so I called the customer relationship centre on *** on the 1st of April 2015 at around 11H10 and spoke to the lady called Johanna mzili whom she was at no help at all for more than 30 minutes on the line. What absurd me is the fact that she said I never change my options during my first stepup in 2012, which I told her I did and have the contract with me, and asked why then my account was never increased every year if that was the case, she failed to explain instead she stand on her words, I'm a very loyal customer for fnb. I've been quite with all the bad services I've been received, it's very frustrating when such a big institution can just wake up and impose the increase on their customer forgetting the contract agreement, as my fixed rate expire on the 19 November 2017, i will never allow you to exploit me.