MTN owe me money and aren't paying me back.

I took out a MTN SKY contract. After a while I noticed around R7000 missing. They claimed it was because i went over my limit. The sky is unlimited. Then i asked for my money back and since then it has almost been three months. They keep referring me to different people but nothing comes of it. Even my local mtn branch cant get them to pay my back. This is unacceptable. Mtn is the worst company I've ever had to deal with.