Upgrade Problems - Summer Mobile

I recently had the opportunity to upgrade my contract with MTN, and received a call from Summer Mobile to assist. I requested delivery of a Samsung Galaxy Tab S 9.7" as part of my upgrade. The couriers arrived a week and a half later with a Samsung Galaxy Tab 7", which I promptly returned. I calles Summer Mobile on the same day and spoke to John concerning the issue, who then assured me that he will assist with the upgrade cancellation. He did inform me that this will only happen once the item has been received back at the MTN warehouse. The item arrived at the warehouse on the 16th of November, and nothing has happened since. Numerous phone calls and threats later, and I am still without any device, and the upgrade has not been cancelled yet. Upon enquiry to speak to a supervisor/superior, I was answered by a "What do you mean, what supervisor?". Today, on the 29th of November, I have yet to hear from anyone at this provider, after being promised by John repeatedly, to keep me posted and to get back to me, and my first upgrade payment has also been paid. I would discourage EVERYONE AND EVERYONE ELSE to NOT take up ANY offer from this company. I will also take up this matter with MTN as I believe that there should be some form of control in place to prevent such serious misconduct. I am seriously appalled by this gross negligence and misconduct!!!