Charged out of bundle, though not connected

I've reduced my monthly contract to save money, but continually need more data, so I buy more. Unlike in the past (just months ago) Vodacom doesn't send me notifications that my bundle is about to expire. It just cuts off and wipes out the data. The issue is that I suddenly get SMS notifications that I'm being charged out of bundle, with no notification that this was about to happen (as my data bundle had been cancelled/duration expired). Even worse is that the out of bundle costs keep increasing, even after my mobile data had been switched off and I've been connected to Wi-Fi (not Vodacom Wi-Fi). I suppose it can be a delayed notification, but doesn't foster more trust in the network and company.