A real billing *******

I have a contract with MTN, the type that has free call time and then it starts charging. I called MTN to set a limit of R10 passed my call time so that they can soft lock my phone when the R10 limit has been reached. The 1st month my bill was +R1900, I called them again to query this and they told me that their limit system is not spot on and therefore is no guarantee that it will kick in immediately as set. I argued the gap between R389 and R1900 was too much so they had ample time to cut my calls but I could see that I was not getting anywhere with them. I was then advised to change my contract to a top up contract so that when my call time is exhausted I can load airtime then there'll be no additional charges for calls. I went to the store and changed my contract. To my surprise , my bill that month was +R900 which did not make sense. This month my bill is +R600 which is still more than my contract with them. <br> <br> They sent me an sms offering me a limit increase from R620 to R3300, I never requested or agreed to the R620 to start with. Their sms said I must reply no if I do not want the increase so my guess is that if you don't respond they give you the increase anyway.