Activation of contract without my consent

On 16/08/2015 I received a SMS from Vodacom saying that they have activated a additional line on my account. I ignored the SMS because I know that I did not activated anything. I thought that they have made a mistake with the number that they have send it to. At the end of Sept 2015 I receive my bill, wich was paid by EFT as usual. A few days passed when I received another SMS from Vodacom with now said I am in arrear on my account. I immediately phone costomercare,stated my problem and block the line. After numerous phone calls to accounts division and customercare, asking them to provide me with details regrading the person who have entered into the contract with Vodacom, i only get the answer to fax a affidavit to the accounts department. To me this answer is not exeptable because now I must proof that I am not guilty. I am innocent until proven guilty Vodacom,this is the law of South Africa. All i am asking is provide me with signature or voice of the person who entered into the contract with u.I also want Vodacom to provide me with the details where I have signed for the simcard,because until today I did not received one. Keep in mind that I have paid my bill every month