child support acknowledge by written request

i have a letter dated january 2015 asking for a child support to my husband stating a child monthly support of 3,000 each child (i have two kids, ages 10 & 6). a letter also stated that he abandoned us, he signed the letter, but until now he has not given a single cent of receipt, he's currently employed. He never tell me where his worked and to whom do he work with, but I sneaked into his things and I found out he's working through an agency which location is at ilocos sur and now he's assigned at vfa...is the letter sufficed enough to demand his support with our children...should i ask for a lawyer to authentic it and ask the lawyer to send a letter to his agency together with the signed letter i had as proof...by the way he got a girl pregnant (the girl was about to give birth this coming May or June),but they are not living together because I think he's afraid that I might file a case with him.