Worst service and worse network ever

I have been an mtn user now for atleast 10 months. I am a regular internet user therefore i receive 2gigs of data every month. I have uncapped internet at home, so my 2gigs of data always lasts. For some strange reason i had 900mb at the end of november , which is quite normal. When i checked again, i only had 200 mb left and 5 minutes after that 0mb. This was soo strange and new to me. I then purchases 100mb just to see what would happen. In 3minutes the 100mb was depleted. Later that same day i bought another 100mb and the same thing occured. This is my problem, i know how internet works, my apps are only active when i am connected to a wifi network.The lady who assisted me told me its because i have an iphone?does she think i am stupid? I know what i am doing . I then spoke to another lady explaining this issue. She gave me a reference number.Dear Customer, Your query has been resolved with reference number 1- ********** 9444. Kindly contact MTN within 48 hours if the problem still persists. Nothing was resolved. I pay R700 a month for this cell phone. I work hard for my money. If this problem is not seen too , i will take this phone back to the mtn store!!!Thats how upset i am.