Poor cruelty service from Dstv

I took a price lock contract with dstv. According to the contract agreement the installation was included in the contract but upon the installation time I was told that I must pay for the installation separately. I then phoned the call center requested them to cancel the contract and they must collect their decoder. Now dstv is charging me for the service that never rendered. Could they please cancel my contract with them please. I am tired with the bad service that dstv is giving us. I have send several emails but there's no response.