help wth regarding legitimate and illegitimate child

good day po need ko po sana nang legal advice regarding this problem..

This problem po arises way back college times before we got married. My husband exgirlfriend claim that the father of her child is my husband. Honestly, we are very confused and were on doubt if this child is really his child. The story goes like this: Naging sila po before naging kami, but my husband and I was bestfriend during that time. after 4 months of relationship with that girl they ended their relationship due to church policy and regulation. Pero on the 3rd month po may nangyari po sa kanila ulit ( sexual intercourse) bago sila naghiwalay. Then sa 4th month po the girl confirmed my husband na safe daw po sila kasi dinatnat siya ng mothly period nya and nothing to worry po daw,And she said that she was dating with another guy. And dignity matters po, inamin po ng girl na mahilig po siya,and shes having a problem with her sexual life,engaging and commting sexual intercourse in casual. and we also both know that fact,tpos po pagkatapos ng two months without communication and contact physically and verbally, na shock nlng po kami na sinabi ng girl na buntis po siya and the father is my husband.
Ang concern ko po the girl is seeking for help financially and asking for justice and support from my husband, sa side ko po wala pong problema tutulong po ako kung anak po talaga siya ng husband ko, ang problema po kasi sinisira nya yung relation naming mag asawa doing moral defamation. So we decided nalang po na mag pa DNA test. but she refuses to cooperate regarding sa DNA testing. And now shes filing a lawsuit towards us regarding RA 9262. tama po ba yun case nya laban sa amin. And ano po bang kaso or RA na pwede ding ilaban sa kanya?? Thanks GOD and more power.!!!!

if he didn't sign the birth certificate, then he should argue that. keep your communication in writing with proof of sending and that she received them.