Bad Service Cell C

I had problems with the inception of my Cell C wifi contract. My contract is ending 31 May 2018. I have informed Cell C accordingly during April 2018 (it was a fixed line at a cost of R200.00 for for 5G anytime and 15G nite data). On cancellation of my contract I received an invoice of R600.00 and on inquiry to Cell C I discovered that the line was opened and not cancelled according to my contract. I am still waiting for my refund difference between the R600.00 and the fixed price of R 200.00. It seems that the contract has not been cancelled as yet. The case number of the dispute is ********** 176