Want my full credit paid back to me

From the 18 December I have being requesting MTN to refund an amount of R1298.00 they have been charging me for though I have upgraded a long time ago. I sent a number of emails and I also called but to this day no one has bothered to get back to me and explained to me as their customer instead they just refunded me half of what they owe me and took the other half to God knows where because it does not even show up on my statement. Yet they are still billing me. I am sick and tired of begging for customer service from them where as they are supposed to provide a service to me. Their customer service is bad and I cant wait until I am done with their contracts. They want their money but when they owe you they don't use the same principles, such double standards. Their agents are so *********** and the staff as a whole dont keep their word. MTN is a lame company that does not care about their customer. All I want is my money back as much as they were able to take it, they must just bring it back. It is my MONEY, NOT THEIRS!!!!!!