********** addition of contracts to my account

I've two contracts with MTN, one voice and the other data. I've not been receiving statements since Jan 2015 on my data contract despite my request to MTN to send me monthly statements. The monthly subscription for the data contracts is R150. In April my bank account was debited an amount of over R2k, and then in May an amount of over R4k. Finally, last week I received statements. As I was going through the statements, I realised that two new contracts have been added to my contract without my knowledge. I brought this to the attention of MTN to investigate and asked that they send me the results of their investigation so I can open a ******** case of ***** and identify theft. I was requested to send an affidavit which I refused on the basis that the onus is on MTN to prove to me that I was the one who signed-up for these contracts. After refusing to send affidavit, MTN is now threatening me that my credit record is going to be negatively affected and they are going to leave the two ********** contracts on my account. How dare can they threaten me? I've now escalated the matter to the CEO, I await his office's response, better yet resolution. I'm taking this matter further...