@kokbashousehold if you click "Change plan now", PM will charge you the amount of the new plan and start the new plan new cycle immediately
Unused data/minutes on the old cycle will be forfeited. No partial refund on the remaining days for the old cycle
And with plan change, any activation bonus, like those 2GB bonus for # months when you activate will be gone as well
On the other hand, add-ons you purchased before, holiday bonus you got from before will be all there still
