Poor service

In February 2015 I called mtn customer service line with regards to my contract that I have with them for cell no ***. I wanted to know if I can change from open contract to top up, the consultant that was helping me told me that I can and I requested the fees for changing and she told me that the system show R0.00 so I don't need to pay anything. I asked her where can I do that and she told me that I can do it to any mtn store. At the beginning of April 2015 I went to their mtn store in East Rand mall to do the migration and I was helped by their consultant with the name Brenda I explained to her what I wanted and I also mentioned to her that i called the customer service first and i was refered by them to the store. I told her that i want the same offer as my other contract which i have with them for number *** and i explained to her that i want a Top up. She did the changes on my contract and she told me that I am going to pay R139.00 per month for cell no *** and the R189.00 for ***. In May mtn took R1900 and June R2600, I went back to the store and customer service up to this day the issue has not been resolved.They making their mistake my problem