financial obligation

good evening po. i am a single mom of a 5yr old boy.. i was never married to his father but he signed the acknowledgement/affidavit of paternity on our son's birth certificate when we had it registered in the local civil registrar. he and his family promised to give support to my son monthly, but that didn't happen. few months ago, my ex and i had a verbal agreement that by the end of every month he will send 1 thousand pesos as his support to our son. and since i don't know how much his income is (and kesa walang matanggap yung anak ko na sustento) i agreed/accepted the said amount. the thing is, i always need to text him about the money every month, because if i wont hindi sya talaga nagpapadala even though we had agreement. and he always sends the money late. last month i texted him to remind him about the financial support but he didn't reply, i even sent messages to his mail but he keeps on ignoring me.. until now, almost mid of the month na wala pa din ung sustento.. technically, he is breaking the agreement we had. now, what do i need to do to force him and have him oblige to give financial support monthly and on time? what case or petition can i file and where? he is still single, so more or less how much can my son get, especially now that he is already studying? where do i need to go to get assistance? thank you in advance.

the legal remedy is to file a petition in court for support

so it means i should file the petition directly in the prosecutor's office? no need for me to go to the Barangay, etc. like what i read in other person's case? thanks again in advance. i just really want my son to get what his rights are.

no, what i mean is a civil case for the court to fix the amount of support.

thank you very much..