I think money is only taken directly from his wages by the employer when the person has been non compliant, this is the case in my experience anyway. We also had the same problem and after getting no answers from the employer on the phone the csa sent someone round to investigate. My blokes ex had the wages person helping her to scam the csa by passing fraudulent info to them about how much she was earning. Hopefully you daughters ex is not this cunning.
Unlike someone who pays willingly, who pays a set amount every month regardless of it being a good or bad month for them, people who have their money taken by their employers have to have to earn over a certain amount before they can take the payment. So say the amount they must earn is 400 (for example, sorry I have lost the pound sign from my keyboard) and the amount he is supposed to pay your daughter 100. If he only earns 450 that month she will only get 50. Is it possible he is earning less that he was?
The only real way to get the csa to do anything is to get annoying. Phone all the time and annoy the sh*t out of them and if that doesn't work make a formal complaint. This has worked for us (almost, getting there). You will also get an individual case worker this way so you deal with the same person all the time. For their staff to say she should not rely on the money is terrible, thats their job. There are alot of crap people who work there but make a noise untill you get someone good. Sorry if you know all this stuff already but honestly, make a complaint and keep rininging them. If you get someone crap complain again. Eventually they will give you someone who will be willing to make an effort to help you. Good luck! x