Breach of Contract with ****** Phone

My wives phone *** was ****** in the afternoon around 15h00 on the 24 of July. She tried for more than 4 hours to contact customer service to block the sim card but nobody answer on the customer care line. The next day 25 July she went to a MTN shop to block the the sim card ref no ***. I receive a text from MTN the morning of 25 July that I have reached my limit of R2700.00 and cannot make any more phone calls.The contract for my wives phone is on my name D.C. Oosthuizen. The people that have ****** the phone used it according to me to the limit that was on the contract because of the sms I have received from MTN. The end of August MTN subtract R26000.00 from my account for the bill of the phone with the number *** which is my wives phone. I immediately went to a MTN store to report this and open account query with ref no: *** till today I have no feedback. <br> The lady show me that the phone was used to make International calls and she also show that the phone was open by MTN to make international calls on the 7th July 2015 without my permission. She also said she cannot understand why the limit of R2700.00 was over ride. MTN have to pay me back my money.