Contract upgraded without my consent

I am so livid. I have a router contract with Vodacom which was upgraded without my permission in May. I’m only noticing this today when my debit order seems a bit higher than normal so I called to find out why this is the case. I was then informed by a polite consultant Sphamandla that my contract is on an open plan 20Gig. I don’t recall agreeing to this upgrade as this is a router contract; so where exactly did they get hold of me. So I have been asking for calls recordings that put me at ease to my “contract agreement” for this upgrade. I have been put from consultant to consultant and nothing is resolved. I was then informed to call Rewards on ***which I have and they not helping me because their calls keep cutting but they don’t call me back. I’ve called them 3 times and with each and every agent nothing lodged which means I keep repeating myself. Can this please be addressed because I am ready to cancel this contract.