The CSA are only competent for straightforward cases only. Anything outside the box or a bit tricky - forget it or face months of stress and grief.
You have to pick your battles with them. In court, father of one DS, stated he worked a six day week, but denies it to the CSA. They say that what he has sworn in court is not enough. Yes, really.
If I want to pursue it, I have to find out who he works for and if they deny it, then thats that, because they always believe the employer.
I have been getting £5 per week since November and now will get £32 per week even though this appears to mean he gets paid below the minimum wage.
Basically, they like an easy life and will put you off if they can.
As already suggested, your best route then is to say you want to make a complaint. This means someone will ring you back (saving you the cost of their usual lengthy phone calls) and it will be looked into. This does not mean they will solve it.
I have had a particularly gormless staff member accepting someone cannot ring them back regarding wage details because they have gone to Scotland for three weeks and no-one else in the firm can work the computer. Or, they have put their coat on, logged off and therefore cannot tell them the answer to the question until the following week. This is while the child waits for the financial support it is due by law.
You can ask them to look at an ex who has a certain lifestyle, but no income to match. This is not that easy and you have to have good evidence. I failed because the £25,000 he stated he paid for his wedding and honeymoon "could" have been paid for by his parents. You need plenty of evidence and a good staff member (there are a few) will guide you. I was told to reapply with better evidence.
They will even tell you themselves to take what you can and avoid the stress. Not good enough I know, but sometimes sound advice.