Tough spot! First research your state's family laws. May take some time but old posts here give web addresses and you might try Rosen.com....not sure what states are covered there. Consult a lawyer...most states have some type of lawyer referral program for people not in position to pay full price..try your yellow pages. Regardless of his threats...you need to file motion for whatever you want, unless you get lawyer and start some negotiations that way. Start documenting now...what he pays or not, time he visits with children, phone calls with you, allegations of telling child truth. Problem is, he signed birth cert...now it may just be a battle of proving whether he knew paternity prior or not...if children are older(1s not his) and he has an established father child relation with them, court can still order that he pay support...he kinda did accept that responsibility when he signed birth certs. Don't let threats beat you down or scare you into not fighting for what you feel is best...thats the whole purpose of the threats. If he is slimy & tells child not his dad...you will be able to handle it & help your child through it & it will only work against your ex. Some lawyers will give free 1st consult & even if you don't hire, it can help you get idea of your position and where to go next. Be sure and check your state laws specifically concerning support and non bio dads that sign birth certs knowingly...though lawyer may give you faster answer & results. Good Luck.