Call 211 or 7301000 and let them explain to you where that 300 pesos came from.
I have a hunch that 300 is for GadgetCare, which is your phone's insurance (which is different from the manufacturer's warranty, this actually covers, lost or stolen phone). I believe that for the first month you have 1 month free GadgetCare, and it is part of the agreement. You can have it removed without any penalties, but if you remove it you will lose the phone's insurance (just to emphasize, the warranty is different from the insurance).
Hope this helps.