Deducting money *******ly

I signed up with Cell c in Dec 2013 with the agreed amount of R169 per month. In February 2015, they deducted R179 from my account. I sent in my query about this and they said they sent me a notice about it and \We are entitled on written notice to you (done on 06/02/15) to change the terms and conditions of this agreement if necessary"<br> 1) I NEVER received such a notification<br> 2) Any legal and binding contract may only be changed if BOTH parties agree to the change<br> 3) I never agreed to any change since I was never informed about it<br> 4) The have not even told me what benefits I will be receiving from paying a higher tariff. I refuse to pay a higher tariff if I'm not getting any benefits from it<br> 5) I've sent in my query on the 2nd of March"