Faulty decoder

Bad service I have received so far, I purchased an Explore Ultra decoder with them last year in November. The decoder only worked for a few days then suddenly send out an error that read "decoder doesn't have a working hard drive" I have been in communication with the. Regarding this query ever since and nothing has been done, they have been deducting every month and I have been paying DStv for the PVR functions am unable to use due to their faulty decoder. I have emailed, phoned in and even send texts on whatsapp I get no responses, no feedback, IAM gatvol of this company I want them to take back their faulty decoder and stop the debit orders, coz it seems they don't want to stop the subscription when I contact them an yet they not keen on attending my query