MTN un-authorised deductions

I receive quite frequently these "thank you for subscribing to MTN service" messages in the form of SMS , these services can costs anything from R 3.03 a DAY - and the problem is that I have NOT subscribed to anything. Then you have to dial *155# to have this cancelled, and in most cases you get a "system unavailable , please try later" message. The USSD service actually works, only when you select 1 for CANCELLATIONS, that you get this error message, very convenient ! I think this is ******* - MTN DO NOT HAVE MY CONSCENT TO ADD MONEY TO MY ACCOUNT ! If MTN wants money, they must do it in an honest way, do marketing, and if someone accepted by signing a contract, then you can charge them, taking money which I have not agreed to is *****ing !