How the cut-off date was determined was a question nobody really bothered to ask as Globe would bill us anyway on each day we our plan is active regardless of the assigned cut-off. Our suspicion is that they assign it as close as the activation date as possible or simply when they get all the records straight.
Globe would just pro-rate the charges since day 1 if your plan was activated outside your assigned billing cycle. In your case, the prorated charge was from the period Sept 15 to 17 (3 days) which is not 30 days. If I am right, you were also charged from Sept 18 to Oct 17 (1 month) which would now be your regular billing cycle (your cut-off would thus be every 17th of the month).
After that 1st bill, your subsequent bills would reflect your regular billing cycle (1 month) with a cut-off date of every 17th of the month.
For some reason that you may want to change your billing cycle, you may do so by going to a Globe Business Center or registering to "My Account" on the Globe webpage.
Thanks for some clarrification. You're right that I was charged on sept 18 to oct 17. Just to clear things more, I received my 2nd bill with bill period sept 18 to oct 17. But on the mrf, it shows that I was charged from oct 18 to nov 17. Does that mean they charged me in advance?