DATA DISSAPERAING AFTER 2 DAYSOF PURCHASE!!!

I have been having endless problems with my contract phone where my data just dissapears after 2 days of purchasing. I get my normal bundle on the 21st of every month, 2 days later I get an SMS to say data is expiring in 2 days & 2 days later my data is gone ( i don't download, not really on FB ,only wattsup is active) I have tried ENDLESS times to get hold of MTN, send emails & have been to the Canalwalk branch 3 times last weekend( Friday, Saturday, Sunday) and no one has come back to me & everytime the consultant just loads more data on my account ( which gets deducted when debit order goes through) & tells me to wait for customer service to call me back. THIS IS REALLY UNACCEPTABLE. For the month of June I bought over R 500 worth of data extra & every 2nd day what I have expires. I bought another 1gig on Sunday, got SMS this morning to say it is expiring in 2 days ( at this moment I still have 992 Mb left & 1,024 gig ( night time data) that has not been used...... really loosing that in 2 days time is not on..... IF THIS HAPPENS BY SATURDAY I AM GOING BACK TO MTN TO CANCEL MY CONTRACT THAT I HAVE FOR THE LAST 15 YEARS.<br> can someone please come back to me URGENTLY!!!