MTN also allocate the newest bundle first, see here.So is there a confirmation on the "your current bundle is used up first, before the previous months rollover data is used" thing?
MTN sure don't do that, i don't see how Vodacom can do so either as it will only cause major issues down the line ..both in the marketing dept. and the billing department followed by a whole bunch of irate customers who feels they're being cheated.