Need clarity

<p>So I have a contract with Telkom. Recently I recieved a statement with additional charges. When I enquired Telkom told me they sent me an sms to which I NEVER RESPONDED. This then meant they would increase my limit automatically. How does this happen without me requesting or accepting it? Can someone explain to me why changes are being made to my contract without my permission? I'm seriously upset because the agents arent very helpful either and they keep promising to call me back, needless to say, I never hear back. </p>