BAD SERVICE and ABUSED OF DATA

I think that MTN is *****ing Data from us. I mean how could you use 3gig of data in 3days without even downloading apps or anything. like the other day i had 500mb left in 30min time i got a message from them telling me that my data is completed and to top it all off they USED MY AIRTIME AS WELL.THATS THE MAIN THING ABOUT MTN THEY DONT WARN YOU YOURE DATA IS ALMOST COMPLETED THEY USE YOUR AIRTIME FIRST AND WHEN YOUR AIRTIME IS DONE ONLY THEN THEY SEND YOU A MESSAGE SAIYNG YOUR DATA IS COMPLETED.