MTN ZTE ****!!! I***, BA***

MTN ****, I am using an MTN ZTE router which I have been contracted and only signed an agreement for R329 monthly which is a debit order into my account, yet I have received sms informing that they will deduct R471.15 on my account on the 25 February, what the hell is that??? I normal don't even finish my data on the monthly basis and I asked that they shouldn't think on my behalf and due any increases....I am fine with the contract as it will give me enough Data....so they send me an Invoice with R 471.15 and plus I have to pay the R329 .00. I did call them and been transferred to Billing department and they give me Ref: ***. I need to be refunded my money please and if not I will cancel the current contract and go somewhere else where I won't be charged for something that I never signed for....on the Invoice they wrote : Gamer+ Daily charged 2.63 and I don't play any games. during the night my device is always switched off! so tell me how how such things can happened I live alone and no one or whatsoever can be able to access my modem.