Credit score done ny Financial institution

I have personal loan with Standard Bank, what puzzle me is the interest rate changed on my personal loan of 21 %. When I check my credit record with Direct Axis or Credit bureau it indicate as very good. I have a qualified degree in Accounting and have more than six years with my current employer. I would sincerely wish I can be given a proper explanation in writing on how my score was determined to be given such an exorbitant interest rate. Thank you in anticipation for your assistance