Fourth time MTN cancell's my 500MB Data *******ly

Previous reference numbers refers: REQ:***, REQ: *** & REQ:***. This is the fourth time MTN cancelled my 500MB free data a month as per my signed-off contract. April 2015 and May 2015 no free data. WHY do you do this MTN? Who gives you the right to do this. You have apologised 3 times and said the system has now been rectified, yet again you take away my free data without informing me. I have a contract with you. How many other clients are you doing this to without them knowing about it? I guess I will have to wait another two weeks for a response as per the previous three calls??? Please credit my account for May 2015 with 500MB which is current and give pay back my April 2015 500MB on my May 2015 account too. I am again waiting in anticipation for your reply.