Over billed

I've been a loyal customer to vodacom for years but I have never had to dealt with such an unprofessional call centre agents ever in my life, after being badly advised to make payment on a contract that was ending within the same month and paying it upfront for it, Vodacom still billed me the the amount that was cancelled and payed for. Called their call centre to query my accounts - one of their agents saw the problem and I was promised that the matter would be rectified and that His supervisor would call me back, till today I await for that call. After days I still called them to query all my cancelled contracts with them, I was taken to and fro from all their departments without any help of some sort. I emailed them all the cancelled contracts proof of payment and quotations received from them. Today I sit with a new contract that came with a device - that was never delivered but I'm paying for it. Still vodacom passed on the blame to departments and this matter till today isn't resolved.