Mtn *****ing my money.

I have a contract with Mtn for R760 per month. The first month I went out of contract I was charged R5753. Then the next month after that I was charged the normal R760 again. I have tried everywhere to get an answer on this matter. Even emailed head office. Not even a reply. I have used this service provider for 14 years. I am so disappointed. Vodacom here i come.