Wrong Bill

My invoice amount was R1200 because apparently i went 5gb over or asked for 5gb extra...I have a cap on my data services and have to manually purchase once this has been used...I was told i would get an answer within 24hrs...4 days later no response....THey said even if they find a problem the refund takes 21days??? How can you make a mistake and wrongfully debit someone then say they must wait 21days to get the money back that they wrongfully took????Is this not *****ing???? Most useless company in the world...This is *******!!!11111