Oh sue, don't cancel CSA. That is exactly what he wants you to do. I have suffered the exact same thing for the past year and he used the fact that I was still in love with him to emotionally blackmail me into not claiming money. Whenever I backed off, he was lovely to me and kept in touch and tried to offer help ( not financial) I thought that was better than nothing. Since I discovered all his lies ( he has a job on the side, so is not 'poor' and has now got another woman and let's her kids call him 'dad' despite him saying to me he 'hates kids' and that he could never be with anyone else after me) I have been strong and forceful and motivated to be unafraid of him. Not told you guys on here but he actually posted on his blog page, (day after I contacted CSA) that he wanted to shoot us and have the wisdom to hide the bodies. He later retracted it and said it wasn't meant for me ( yeah right) when I called the police and also told his new woman about him abandoning his child ( sadly for her, she has ignored me and believes that I am making it up and don't actually have a child!?. LoL ).
So...no matter what he says or does , don't listen. That is their game. Threaten you to back off. Nothing hurts them more than a big dent in their pocket. Your child needs financial support and it's the law that he provides it. If you are worried, call the police and social services and tell them he is blackmailing you, tell HIM you will do this if he continues. Better still, next time he gets in touch, tell him you will have a nice word with his 'wife' ( if you haven't already? ) and show her evidence and tell her all about his indiscretions. ( in some cases, CSA payments can be hidden from wives, so don't think just because you are moving forward, she will find out)
Play him at his own game and firmly and resolutely tell him that you will not be blackmailed and he will not have access to your child, ever.
Be strong, you can do it. If I can do it ( and I backed off for so long) then you can do it too!