I have spoken to my son and the information, as far as he remembers, is as follows:
The CSA contacted him in 2004 and told him that he owed £3000 for his son. The story they had from his ex, Claire, was that my son had left her when the first child was 6 months old. However, they lived together for another 4/5 years and Claire had two more sons with him. In retrospect, my son believes that she might have been having an affair for some time before eventually getting rid of my him. The two boys looked like him and he had no suspicions at the time. All three children were registered with him as the father and with his surname, although Claire has since changed their name to her maiden name.
Because my son was out of work quite a lot of the time after losing the children, the CSA took money straight from his benefits and he assumed that they had continued to do so. He suffered quite a lot of mental health issues after he lost this sons and he was homeless, depending on friends for their help. Because his name had been removed from the joint tenancy, he was no longer able to get social housing . He has a narrow boat, but had gutted it with a view to rebuilding the interior.
In 2012 he had agency work in London for the Olympics. It was a zero-hour contract, but obviously was a paid job. This was when the CSA contacted him again to say that he owed £20,000 and they put a rolling charge on his pay, allowing him only £71 to live on, including petrol to London. He did not wish to work long hours for so little money, so stopped the agency work.
Now that he has a permanent job, he wants to make an offer to pay, rather than have a charge on his income, and would also like to find out, if possible, what the situation is with his sons; ie whether they believe the second man to be their father. When Claire sent him packing too, in favour of yet another man, he wrote on Facebook that he had lost his sons. Whether he believed them to be his, or whether it was just because he had brought them up for many years, we don't know.
With regard to the CSA, my son believed them to be taking money from him, but has no proof. It is strange that he suddenly owes £20,000 if that is the case.
The proof that he was still with Claire for a further 4/5 years after their first son was 6 months should be in the tenancy agreement. My son had a bedsit through social housing, then when Claire became pregnant, they were given a two bedroom flat together, followed by a house when she was pregnant with the second child. Unknown to him, Claire took his name off the tenancy, I assume by falsifying information, but he doesn't know when.
I knew very little of this at the time, as Claire had decided to not allow me to see the boys. I didn't want to upset the applecart for my son, so I stayed away until he came to be after the split. I was working in social work and felt that I was doing the best for the children and my son by keeping to her rules, although it obviously upset me greatly at the time.
This all sounds very complicated and I don't know whether the situation can be easily resolved, but I would welcome your advice as to the next step, with minimal available funds.