Absolutely frustrating and terrible customer experience with no resolution in sight

I have added another contract onto my existing contract ***) where I pay R406, and now added R598 to this which is the new contract, totaling to R1004. The order was duplicated and I received 2 orders, which I have returned 1 of them, but my invoice still shows the both lines are active, also adding to this issue is that my payment method changed to cash, which I have never agreed to, and now I am in arrears with an incorrect invoice. I have been on the call for more then 2 hours with 3 different Vodacom agents (Customer Care, Billing, Collections) and I have been pushed pillar to post and no resolution in sight, which is extremely frustrating. I want to pay my account, but I need my invoice corrected and the duplicate amount credited, to make the correct payment...but no1 seems to help me and now I am in arrears but I am a good paying customer !!! I am demotivated and cant believe what I am going through with Vodacom. can someone please help me rectify this, I will not be making payment until my invoice is rectified.