Overcharged for data usage which should be capped

<p>For the last I don't know how many years my payment each month has been the same because I do not want surprises at the end of the month with bills and thus only have top up tipe contracts. Then suddenly this month my bill is 5 times more. And they say it is because of the one number (which is the data contract for my ipad) used up the bundle and they then charged me out of bundle rates. The thing is that that contract was never a contract that should be allowed to do that. It should stop working until you top up. I have never before had this problem until now. And now I am R5k out of pocket because they didn't cap where they were supposed to.</p>