OVERCHARGED ON MY ACCOUNT

I had two contracts with MTN, the one for phone and other for data bundles. The sim card for data bundles I was not using it often then I made calls with it in March and early April but very few call in April. Then I got a statement where I was charged for +-R500. I enquired about this and even requested an itemised billing for both months for the data bundle contract because I knew the callls I have made could not mount to that amount. I was promised that I will get it but its been two weeks since I have been waiting and there is no response. I even terminated both my contracts and when I dial 808 I do not get assistance becuase it is a prepaid number.