Mtn *****s my money, wont give it back

I have a contract with Mtn wich is costing me R250 a month. On the 25 June I find out the deducted R1200 from my account wich is a lot more than what was supposed to. I went to their branch to enquire and was told that i did an upgrade and extra fees are always charged when doing this. He however said that it would not be more than R200 wich i understand. 250+200=1200 is what i dont understand. I was told that the difference would be paid back to me within 7 working days. After 9 working days there still was no sign of my money. Again I went to the same branch spoke to the same person and was told the money would be in my account 15 June. On 16 June still no sign of my money. Again same branch same employee. Still no reason was given as to why this happened in the first place. It is 23June still no money in my account. Can I lay theft charge against them because I must now suffer because they stole my money. Even if they give my money I would like someone who is empowered to look into this. Can u imagine how much money they have at their disposal if they do that to say 1million customers every month. Help me please