Absulute ripoff from vodacom

I have upgraded my acount with vodacom then they said i still owe on my old devices and that i will have to pay extra for 3 months there after. For my old device before i would be charged the normal subscription for my contract packige. Ive tried multiple times to ask for a detailed statement to see what i still owe on my old device and all i get is an invoice i was told that end of march would be my last instalment yet im still getting billed for the old device and to top it off acording to the consultant i spoke to last there isnt a way they can send me a detailed statement just an invoice but i dont have to worry end of march would be the last payment on my old device. This is absulute bull seems like you would have to pay into infinity without any direct awnsers.? I wouldnt recomend vodacom contracts to any one.