Over-billing no response to query

My cell phone bill has skyrocketed in the last three months. I have not used the phone differently in these months so the bill is strange. I contacted MTN on twitter and I called 083 1 808 for help. I have been told it will be investigated on Twitter but I have heard nothing since and again this month I received a bill of over R1000 which isn't normal. When I called MTN I was told it would be investigated but I have heard nothing. The most frustrating thing is that this exact thing occurred at this time last year and after investigation it was found that there was an error and I was refunded the funds. Please would someone investigate what is going on and then get back to me! Radio silence is so frustrating and I know there is an error with this account. The query is for April 2015, May 2015, June 2015 and July 2015.