Vodacom starts a new contract without my concent

Vodacom decides to take it upon themselves to start a new contract for 36 months. My account was in a bit of arrears. My line was cut at the end of last month. The account was settled straight away and I was back on track. Thinking that all was in order, I went to the Vodacom shop over the weekend to make a payment and enquire about an upgrade. Sorry you cant upgrade!! A new contract was started from last month for the next 36 months. This mind you was done without my consent. I am paying a new contract with no option to take a new handset. Vodacom this is not allowed. I want my contract back dated from when it was last in affect and I want to be allowed to upgrade my handset, otherwise I will report you to the NCR for starting a new contract without my signature or consent