Phones not answered, can't cancel contract

I received a call about a week ago from Selldirect as my Telkom Mobile contract is about to expire. The contract was for a router plus a 5GIG data and 5 GIG midnite surfing. for the past three days Ihave been trying to get hold of Sell Direct on *** but this is mission impossible as their line rings and thereafter gets cut off. I am no longer interested in this contract as I will not do business with any enterprise does not have a platform to listen to its customers. I want to cancel the telephonic contract that I made a week ago with Sell Direct and this is solely due to their poor service in handling customer queries.