SMS CHARGES

I have an American Express Account and on checking my monthly statements, noticed that I was being charged for SMS's being sent. On enquiry with the call centre, I was transferred from one agent to the next and not one could answer my question - why was i being charged for SMS's. I requested that the application ( if there was any ) be removed off my account and was told that finance would need to get back to me. I was given a reference number and till date no-one has had the courtesy of returning my enquiry ( I was told that someone would get back to me within a day or two ) - this is now more than a month later. i do not see why i should be charged for SMS's reminding me of my instalments due as my account is not in arrears - and the agent confirmed this. Surely I have the right to manage my account as to what I should or should not be charged for? I do not want to receive ANY SMS's from them and as a consumer this should be looked into as a matter of urgency.