Theft and mtn

I would like to complain about Mtn, my contract expired and although I was notified about the end date, I was not notified about the fact that a discount no longer app****. This causes my account to be debited R1082 instead of R883, this was after I was told by sms that due to the expiration my contract would be reduced to 740 per month. Customer service was no help, this is theft as it is nowhere stated in contracts that this would happen. Absolutely appalled