shortfall on refund for wrong billing

my previous query attended to but refund fell short of about R 500.00. I received, after a long struggle, a refund for R 1 166.45 yet the total incorrect amount was R 1 666.00( R 850.00+R 816.00= January & February 2016) after contracts were effectively cancelled on both *** and the other one.<br> I am not prepared to donate so much money to a big company like mtn, so please settle and refund this amount as soon as it is practically possible<br> Andrew