Unauthorised limit increase on account

I took out a data sim with Cell C in June this year at the Ballito Junction store and I was very careful to put on a limit so that data usage couldn't exceed what I bought. This past month I was billed a lot more than usual and when I enquired why, I was told that there was a 'limit increase' activated on this data contract!! I had NO knowledge of this and most certainly didn't request this. I went back to the Ballito Junction store and the staff showed me on the account that a Nerisha Gounden had 'increased' the limit' from the initial contract amount which was R299/month to R800/month!!!!! Lee at the Ballito store agreed that this was not supposed to be done as she helped me take out the contract and she acknowledged that I requested a limit set on the account of R1 after the data limit was reached! Obviously I refused to pay for something I did NOT request and had NO knowledge of so Lee assured me she would take it up. I must place on record that I paid my usual contract amount except the unauthorised amount but I get an sms from cell c saying my account is in arrears and would be suspended if not paid in full!!!! Surely there must be some law against this! How can cell c do as they please and increase limits which I have to pay for or get my line suspended! And Cell c debits my account for R70 for returned debits that THEY don't Do!! My lines were suspended today so I felt that I was held at ransom by Cell c to pay for this unauthorised limit increase! I feel violated!! How can this company do as they please with my bank account and do what they want with the contracts I have without my consent!! I was given excuse after excuse for why this was done but never an apology or offer to rectify their mistake! It is ******* to deduct monies without my consent!! It is ******* to change my contract without my knowledge or consent!! Cell c is *****ing money this way!! They bill you for what you didn't ask for and if you don't pay you get cut off!!! Lee told me that I wasn't the only Client to experience this violation!!! So how much money is cell c taking from innocent hard working people and playing god with our money and bank accounts!! What gives them the right to do this?? I had NO option but to pay them today but I feel so vulnerable to think that companies bully people and Yes, ***** from us and get away with it! I am tired and want justice. This isn't right. What is the law on this!