Cell C Continues *****ing From Customers

I wrote to Hello Peter in September 2017 regarding the how Cell C cheated me regarding my contract. They promised to sort the matter out after they ****** my dad +- R4000 and they did not. Instead they debited more than what they were suppose to after I have spoken to the cancellation department numerous of times. What must I really do to stop this, im tired of having to reverse my dads money and being threaten of owing them money i do not owe, where as they owe me.