Being overcharged 3 times the amount

At the end of December I received my monthly debit order from Cell c as usual from my contract amounting to R146.64 which was wrong as I had been paying R99 for my contract as per the agreed amount, so I called in to notify them and ask why I had been debited so much the lady then responds by explaining that my contract is finished and this is the amount my data actually cost but I did not understand why they couldn't have called or contacted me via email/sms to let me know that my contract had finished and I would need to upgrade or cancel the contract and not just taking an amount that pleased them but that's not the worst part. I let that part go graciously and told the lady it's okay can she please just put me back onto the original agreement again and we call all just get on with our lives. When this month's debit order went off it took R310, I was completely baffled. I call in again to get this sorted and the lady tells me to call the sales department and tell them to reverse the money, why she couldn't help beats me. She then put me through to the sales department which she should know doesn't operate on Sunday but she put me through anyway to an automated response.