Billed for SMS to *** which I did not send

My contract with MTN is a pure internet data month-to-month contract. The contract price which I pay per debit order is R 319.00 p/m. When I received my invoice for November 2014, I noticed the amount to be R 319.86.<br> <br> Upon checking, I found a line for Short Message Service to the value of R 0.75. I contacted MTN customer care to find out what this charge was for. I was advised that it was for a SMS which was sent from my number. Since my SIM card is permanently installed in a router, I know it was not possible to have been my number that sent the SMS. (Yes I know there is a option in the router's management software to send SMS's, but I did not use it to send any SMS during that time).<br> <br> I requested MTN to provide me with the content of the SMS, which they never did.<br> <br> We agreed that they will send me a itemized bill for the period, which I will be charged for, but, if it was found that I was not responsible for the SMS, I would be refunded this amount as well.<br> <br> Once I received the itemized bill, I could see that the alleged SMS was sent to number ***. Upon trying to contact this number, I get \The number you have dialed is incorrect. Please check the number and try again"