Imposible to settle a device

I have been trying to settle my device with Vodacom since the 30th of November 2015. I followed all instructions given to me by mail from the retentions and cancelations department. After phoning the call centre on the 3rd of Des the agent told me that they can see the amount has been paid and I need to phone back after the invoices for Nov payable end of Des is released. He told me that should the device still be on the invoice I would need to phone them back to get it removed. Since then is has been a nightmare to get this device, which is paid up, removed from my invoice. They keep on telling me that I have a credit and my total bill will be deducted from this credit, but this is not what I wanted! It seems that there is two things within Vodacom that is impossible: 1. To settle a device 2. To get hold of a supervisor or manager at any department for further assistance. Every time I phone there is a different story and a different department that should help me. They do not allow access to the telephonic recordings to prove that an agent stated that it would be sorted out a week ago and to add insult to injury they have an attitude when I asked to speak to a manager.