Child maintanance without seeing child

I think my ex should pay for his son but he's saying he's not his and wants a DNA test his cousin has told me he only wants a DNA test so he can try get visitation but I told him he's never seeing my son because he's a drug user (weed ,ket and coke) I have videos of him high and multiple people who could back this up so is there a way I can get him to pay and also never see my son?