Extra charges not explained or credited

I recently took out an MTN contract for myself and my wife. We were quoted R38 a month each, all inclusive. When MTN eventually got their act together and activated our numbers 3 weeks after we took out the contract, I received my account and had been billed R156.94 for my wife's number and R155.45 for mine. This may seem like a small amount but we are pensioners and every cent counts. After visiting MTN at Westville Mall, no one could explain the additional amount. My daughter-in-law phoned them and there was no one available on their telephone service to help. She even put a complaint on their Facebook page to be told to send them a message, which she did but there has still been no response. This is the worst service we have ever received from any provider!