For your concern, everything is stated on the bill. Globe Postpaid does not incur any surcharge if payment is delayed. Your bill is detailed and has the breakdown of all the charges that you have incurred within a billing period.
For cases like these, you may have exceeded your consumable amount which then tops-up on your Monthly Recurring Fee (MRF). Plan 1799 is already inclusive of tax.
For further bill explanation, you may want to visit the nearest globe store with customer service so they may assist you personally with the detailed explanation of your postpaid bill.
Thanks and best regards!