MTN pathetic

I have not changed or upgraded my account or device for a few years now , as I don't need the added expense. MTN has been hounding me for months trying to get me to upgrade. I finally gave in an listened to their sales pitch 2 months ago. Spoke to a VERY nice guy who assured me he's just changing my contract so I will pay less ..with no device but extra data and minutes. And should I want to upgrade to a device I could do so at any time. All good and well my bill dropped to R229 ..great! I was saving. Now all of a sudden thus month I have been charged R390!! For what??? Calls and emails go unanswered. I have reversed that debit order and MTN can contact me with their banking details so I can manually pay them the R229 I owe and signed up for