Vodacom upgraded my contract without my consent

I have a contract consisting of three numbers with vodacom, one of the number was due for upgradation, to my surprise I received a message from vodacom last month saying I have upgraded that number and I am owing vodacom R2023,25 (mind you I did not request nor authorized them to upgrade that number as I was planning on canceling the contract of one number) I did not agree with paying that amount, even went as far as going to my local vodacom store and called customer services to lodge a complaint but they were of no use or help so I paid the normal amount I was used to paying of R1780, 00 but now they sent me another statement for October saying I'm owing them R4300. May you please help me to resolve this matter.