Bad Service and unresolved case for 6 months

I logged a case with Cell C in July 2014 and it was resolved by Anthony on the 30 January 2015 when a refund was paid back in my Cell C account. The refund was R280 but was not credited in my account and on the 25th of March I paid R200 to cover my premium. End of March I was told that I owe Cell C R139 .99 when I ask how and why they told me that I short paid in March. I explained what happened to more than 15 people and this case has been escalated more than ten times but I'm still getting threat that I'll be negatively credit listed. I call every week 3- 4 times is a day and I still have no one assisting me. Falls promises is all I get.