Postpaid contract must be prepaid?

I changed my contract to the sky unlimited contract in October. Now I get a R5000 bill because I have to pay my October bill and November bill prepaid or they cut my phone off. This is nonsense! I was never informed this contract is prepaid. I am a top customer that spends thousands of rands every month and I get treated like this. I work from home and now my phone is going to be cut off. As soon as my contract is up I will port to another service provider.<br> <br> In addition I have been trying to cancel my data contract on *** for 5 months and it still reflects on my bill every month. I have called and emailed numerous times and it never gets cancelled.