How should we deal with the CSA?

Hi, my hubby has a child from a previous relationship who he saw every weekend for 12 years with no problems, when he met me she decided to take him to the csa.

Then in nov 2010 my hubby had £113 taken directly from him wages without him even having any correspondence, the csa said he owned £15,000 in arrears??

They told him that it came under the old rules as a document had been sent to an old address that he hadn’t lived at for many years??, my hubby is honestly on the verge of a nervous breakdown, for 2 years he paid £60.00 a week which he paid with no complaints, apprantly his ex had told the csa that he has never seen the child?

Even though we have many many photos of my hubby and his daughter together, even photo’s of myself and my hubby’s daughter, i’m so worried about my hubbys welfare, is there anything we can do??

I also have a disabled child is there a reduction for this please i could do with some advice. Many Thanks.