How does your billing work???

I have two lines with Mtn, one voice and one data. Both line were due for upgrade and I upgraded my data line in store (Centurion Mall) while the voice line was upgraded telephonically through your call centers. However, with the voice line upgrade, I never received the phone but my account was being billed to the extent that it is now sitting with your legal department. What I would like to know is how are you charging me for an upgrade that according to you was never confirmed. I did this upgrade on around April/May and never received the phone. I called twice to find out why I never received the phone and nobody bothered to call me and inform me why the upgrade was never confirmed, yet I am being billed the upgraded amount. Furthermore, on my other line I was even paying more than the installment amount, in good faith. What exactly would I be paying for on the voice line if I never received what I asked for and no communication was made to me explaining what happened to my upgrade. I want a detailed explanation, which includes detailed statements which accounts for every amount charged to my account!