MTN still owes me money

I logged a complaint about MTN that owes me money and they responded by saying they refunded me the R11.40 debit order fee. MTN, please wake up. You refunded me the debit order fee but you still owe me the actual monthly instalment you incorrectly took. You gave a settlement when I cancelled my contract..I paid it and thereafter you still deducted a premium. This was an error on your side according to written correspondence received from your credit department. This is the refund that I am waiting for..not the R11.40. I want my money!!!