Hey Hun! You need to look up the general number for Csa failing that I can pm it to you! Ring them up and give them all the fathers details, they will then contact him and ask him first off if he accepts paternity, if he doesn't they will ask him to pay upfront for a DNA test! If he refuses to they can start the DNA test route and charge him more!! Basically, what my ex was told was its a pretty expensive way for a bloke to delay the inevitable if they know the child is theirs as they start accruing maintenance from the very first time they contact him!! suprise, suprise my ex changed his mind! You won't have to pay to it, the bin resident parent does!!
And yes I think you can put a father of the birth certificate after, not 100 % sure but it used to be the case!
Hope this helps Hun! I'm in same situation xxx