Flash ads killing my phone

I receive flash popups on my phone. This is not a message, push notification or mms. It is a full blown message covering my entire screen and can even turn on the screen. Ive been in talks with MTN for a month now. The problem is each time we get to a point a *********** customer care agent take the call and we are back at square one. The last one even said it is not mtn marketing. Well only the sim card is allowed to display full screen messages as it is supposed to be used by carriers in emergencies. These flash messages is so frustrating and MTN cannot or does not know how to turn it off. I will be moving back to Vodacom next month. What a pity and waste of my time.