Contract change with no notice

My husbands phone is due for upgrade - which he hasn't done yet. He noticed this month that he hasn't received his 1GB data as usual. He phones the call centre to ask and gets told that due to the upgrade being due, he no longer receives the data. Really Vodacom - how do you just do that without notice. Is that even legal due to the fact the no new papers have been signed. As far as I know and experienced contracts do not just change because an upgrade is due. This is really unacceptable especially that not notification was sent through to warn you. I would appreciate feedback ASAP