Breach of Contract Agreement by On-Air DSTV

In April 2019 I was given an offer by On-air DSTV on an Explora3 decoder upgrade for R139pm for 24 months with free delivery and installation. Delivery came but no installation, tried to contact them and also to trace installers on my own but no assistance. Installers want upfront money which is unfortunately not part of the agreement with on air as I was told that my first will be only after installation of the DSTV. Following the delivery of the decoder, deduction by On-air was made to my account, I then reversed my money back since there's a breach of contract by On-Air because the installation is not yet done, I waited for 3 months and still no installation happened, I then told them to fetch their decoder since it's of no use to me. They thereafter kept quiet, did not fetch the decoder and than put me to BMD to collect their money, I've been explaining this to BMD but I keep getting text messages from BMD to bay for On- Air account. I'm so fed up with On-Air I really need to sue them. They are ******. How can they not meet the agreement but expect money for that.