Overcharge interest rate on Credit Card

Standard Bank charges on credit card is 3% higher if your balance is below R10 000.00. My balance was not below R10 000.00 and Standard Bank increased my interest rate with 3% without any just cause in May 2015. I brought it to their attention and they reversed the transaction - just to reverse it again in August 2015 and continued to overcharge me from August to January 2016 when I reduced my credit card to below R10 000.00. Several complaints and phone calls later - I have no joy and nobody seems to be able to correct this - the answer I get is that they are waiting for a response from their IT section!<br> HOW MANY OTHER CLIENTS ARE THEY DE*****ING LIKE THIS AND HOW DO WE GO ABOUT TO EXPOSE THIS ********* BEHAVIOUR? <br>