Service on a contract I didn't request for

Good Day<br> <br> I took a cellphone contract on June 2015 and was paying R589.99 per month ever since, suddenly I'm owing R716.50 due to Telkom adding a service of R200 worth of airtime which was added without prior notice and my consent. I've called the call centre several times and up to date, no consultant is able to give me an answer on why was a service was added without my consent...<br> <br> May I please get an answer from Telkom immediately as this is unacceptable service...