Stop taking my money ********ly (my opinion)

The lowest rating Hello Peter permits is 1 star, this is unfortunate because in my opinion MTN deserve no stars and should also be charged with theft. On 4 May I purchased R100 of airtime (pay as you go). This purchase was made at an Absa ATM, a simple confirmatory SMS was sent to me advising of the airtime top up. Today, 9 May, after only making about 2 calls and sending a similar number of SMS messages’ I noticed that my airtime is now R0.00 (NIL). This is impossible. At no time during my airtime purchase or after did I enter into any other agreement or otherwise give permissions to the contrary about the nature or use of my purchase. In other words my contract, like always, was to purchase airtime and airtime ONLY. Any deviation from this is a manipulation of what I purchased and clearly not what I wanted nor requested. In short what is MTN going to do to reimburse me with my proper account balance less the odd outgoing phone calls made etc?