C.s.a. Advice Wanted

[youngie]

I seperated from my abusive, drunk ex-husband nearly six years ago. I had two children with him. We all had to up and leave our home and move to a strange town to get away from him. The children have not seen or heard from him since (his choice).

Six years on i have a new partner and another child. We are on income support, of which the C.S.A. send you forms to fill in about the father of your chilren ect... which i had to do, no choice of mine.
The next thing i hear is the C.S.A. have contacted my ex-husband and now he blames me for the C.S.A. and is thretening to cut my parners and familys throats, and that i have to call off the C.S.A.
Then i get a phone call off the C.S.A. saying that my ex-husband has denied the children are his, and now we all have to go for a D.N.A. test, do we have to??
If so i know he is their father and then he will have to pay for the D.N.A. tests too, which will set him off again, what do i do??