Incorrect Debit Order Amount

MTN took almost double premium of my husbands MTN contract. We went into the branch and the lady told us we must phone on 083138 on Monday, she said that there is a los of clients complaining about the same thing. My husband phoned, they told him that MTN send him a SMS in October asking if he wants to keep his limit on his account or if they can make it an open account, he never received the SMS. MTN then just went ahead and made it an open account. WITHOUT ANY PERMISSION. The lady said that its for the airtime and data that he used but why when the data and airtime he received was finished he had to buy again? So who used the airtime and data that MTN charged him for? This is unacceptable. We are both loyal customers to MTN for many years now but after this we are really disappointed.