MTN charged me for a promotion they ran, which was meant to be Free!!

I signed up for a contract upgrade with MTN last year. My package was/is to receive 350 minutes, 1GB data and sms's for R579 per month. They were at the time running a promotion where I would get "free" 200 MTN-MTN minutes and 2GB of data for a year. When the period of the promotion ended, MTN failed to stop the free minutes and data and billed me for them. I got a bill of R999 at the end August. I was shocked and called their call centre, one of the many agents I spoke to said the mistake was on their side and that I would be refunded. The did refund me about a month later after countless follow ups. To my shock and surprise, they again debited my bank account for R999 at the end of September. I called again and they gave me a ****py explanation that I didn't understand, but I decided to let it be as long the debit orders went back to my contract amount of R579. To my further shock and surprise, that was coupled with disgust this time, I was debited R832 this month, and when I called, again I was given a ****py explanation about them having ran a credit on my account in the previous month or something like that. I'm appalled by MTN, and so much that I cant wait for the contract term to end and I get out of MTN completely. The inconvenience is just too much for me to be happy and continue as if things are fine.