kdn you can call 211 or 02-7301300 to downgrade your plan since you are already out of contract. If the "Plan zero" is still available, then you can have it to retain your number. Otherwise, the lowest plan now under myLifestyleplan is 499. Just inquire with the hotline for your other options.
Ask about the 0 plan (pay as you use). There is a Php 50.00 monthly charge for maintenance of the account.