Unjustly debited

I closed my Cell C contract off by paying off the commitment amount that was left and by also including the amount of money that needed to be debited at the end of the month. They still debited me although I paid the commitment amount and included the amount that was due. Now they taking too long to pay my money back, they say they have a case running but that case been running for too long. I just want the money that's due to me, they took money that's not theirs and now they are giving me stories I'm not interested In.