Multiple frustrations with Multichoice

In February I contacted DSTV about taking up the offer of the latest Explora (with Access fee included and free installation and delivery) at a cost of R899 per month for 24 months. I have phoned and emailed DSTV multiple times. They have it on record that I received the decoder and that it has been installed, but I have neither received it nor has it been installed. Now they want to bill me for it! When I phone, I am told my complaint will be escalated but nothing happens. I was given an email address to cancel my order but it bounced back saying I was not a valid user. It is impossible to speak to anyone with authority to help.