Ok, this is what my husband just emailed me back:
Thank you so very much for asking your husband I feel so much more confident about ringing them now. Im still new to all this stuff and not 100% on how everything works.

He was reassessed in August after I asked them to because he was only paying the bare minimum and they found he was earning significantly more and his child support was adjusted accordingly. This made him really upset and thats why he was crying poor to csa saying this new amount would be unfair cos he had so many outgoing expenses. But I think if you can afford a trip overseas for 3 weeks you must nt be that bad off.

Thanks again