Had a child nearly 3 years ago. But my ex dumped me when I was abwt 2 month pregnant never was involed much. He was at birth and is on birth cert. lucky if he has seen our child hand full of times and last time was over year ago.. to which child doesn't know who he is any more. Reason for not being in contact is because he say the child isn't his and demands dna. To which I have offered few times but he never shows. But then got in touch out of blue demand one.where do I stand

It sounds like you are somewhere in the UK? (It matters)
If you don't want to do this willingly, he has to go to court to order the DNA test. You would then, based on the results, go to court to file for child support! He can't have it both ways.

I do get csa but try to cancel it loads of times.. with csa and don't mind doing one as have nothing to hide.. but why does he feel the right to start playing daddy after this time.. when my partner has always been there still 6 month old