Cell C Disgusting Service

I enetered into a contract with Cell C for internet service for 40/20Mbps and I pay R999 per month for this service. Over the last two months the service is less than 1Mbps. Sometimes slightly higher but the service is disgusting. I have emailed twice over the last two weeks to the customer service with no response at all. They take my money but do not deliver their end of the deal. Even worse just ignore my appeal for help because I cannot enjoy the service I am paying for.