Overdraft interest rate doubles without warning

<p> </p> <p>Interest rate that I have been paying on my overdraft was 8% and it has suddenly gone up to 22%.</p> <p> </p> <p>Strangely - there's a 21% rate deduction on my current account and a 22.5% interest rate on my RCP. I don't know why I have multiple interest rate deductions, different and exorbant rates because the Standard Bank website actually says "the prime lending rate is 10.50% effective from 18 March 2016". </p> <p> </p>