Standard bank cant even do simple math

On my current account statement dated 22/07/2015 the interest rate I was paying on my overdraft was 15%.<br> <br> Then the rate went up with 0.25% end of July. <br> <br> Now the rate I am paying is 16%. How on earth do you add 15% + 0.25% and get 16%????<br> <br> Are you cheating or just not very competent? I send a secure message to Rivonia Branch last week and a woman phoned me. After I explained, with difficulty, the issue she promised to phone me back. This was last week. Not a peep since. <br> <br> Standard Bank, please resolve the issue. In case you don't know, 15% + 0.25% = 15.25%.