Bad service complaint

3 months ago I downgraded my contract. I am still being charged for the higher amount. I have been trying to contact Cell c on 084143 for the last 3 months but they do not answer the phones. 3 times in 3 months I got hold of them. 1st time to downgrade., 2nd to complain that it wasnt done 3rd time again it wasnt done.. my original contract was R1099. I downgraded to R269. For the last 3months they are still deducting R1099. On the 29th Aug I spoke to a Bongewe who assured me the refund will be done....still waiting. On the14th Sept I spoke to Manape....once again apologized and assured me the refund will be done. For the last 2weeks I am unable to get hold of Cell c they just do not snswer their phones. What must I do to get this matter resolved???? My reference no for the last call was ***0.