Heh, i don't think it's related to that. It most likely means "we are going to charge you, and your current account will no longer exist if you change your mind, so you can't reverse this action and get your money back" . You can still cancel whenever, you just can't simply switch your account around every week and expect to pay once.
Basically if you're on 5GB and upgrade to uncapped, and you use 10GB, you can't then just switch back to your original 5GB account and get your money back midway through the month. You'll most likely will have to either
a] Cancel your uncapped and recreate a new account (i.e 5GB account)
b] Downgrade at the end of the month for the next month
Even Telkom ISP work like [a] . If you want to change your bundle, they actually cancel your current one, and create a new one. So i assume this is what they mean.