I have effectively given up with the CSA, and have also had the conversation with them about not contacting me anymore rather than feebly trying to extract any money out of xp.
My xp is a serial job hopper.
It takes the CSA approxiametely 12 weeks to trace his latest job through the HMRC, yet he is very rarely in a job more than 6 weeks.
The last time I rang them, he was working for Bob the builder, and they promised to look into it.
They called me back 4 months later to say they had written to Bob to ask for details of his pay.
I told them he no longer worked for Bob the builder, and hadn't worked for Bob for 3 months.
I explained that he had since worked for Handy Manny for a further 5 weeks, before leaving that job, and going on to work in Big Cook, Little Cook's kitchen before he got the job he was at now, working as an Imagination Mover.
They have managed to catch up with him once, at which point he said he would pay me directly, and they said 'Erm, ok.' Of course, he never did.
They can never tell me anything useful either because it always comes under the data protection act. 
I honestly think the people who work at the CSA have lost the desire to nail the feckless non paying bastards, because they deal with so many and time and time again obstacles are put in their way.
I hate xp for depriving DD of financial support, but I am full of rage that the CSA can seemingly do nothing about it!!
In fact, I am so angry, I sometimes find myself laughing at their feeble attempts to get him to pay now, and that's something I thought I would never do.
There is no respect for the CSA, and no fear of the consequences of not paying.
My xp sees them as an annoying gnat..brushes them away and forgets about them. 
It would be easier, I'm sure, to get blood out of a stone.