Ridiculous bank chargws

I have never felt like this before. I woke up to an account sitting on a negative almost R800. How possible is this? This bank never rewards me when i am sitting on a positive amount by the end of the month with that amount of money and yet has the nerve to charge interest of that much? If these charges are not reversed by the end of the month i will move my baking to a provider which takes care of its clients. After banking with absa for over a period of three years its the first time I'm experiencing such. I am not a happy customer at all. Please attend to this ASAP.