Why do CSA only think of themselves?

I have a very bitter and twisted ex-wife , a few years ago we had a big argument and she stopped me seeing my son and I have no relationship at all with him now .

Before this argument I had my son regularly , took him on holidays , days out , bought him clothes , presents etc and had a strong bond and fantastic relationship as a father and son should have and I never asked for any money from my ex-wife . Well after that argument she sent me a text saying ” karma ‘ is going to get you , in other words she was going to do something , well I got custody of our other two sons as she is a poor mother and they did not want to live with her so now they have both left home and are now 21 with there own lives .

I had an accident in 2011 , I have suffered with depression , had to go through four operations over the four years I was out of work and because of this we are heavily in debt , I told the child maintenance service this and according to them this is irrelevant , I am approximately

£65,000 in debt and they have said that I have to pay over £400 per month and because of this I cannot afford to pay my creditors, my ex-wife has done this purely out of spite and bitterness , she has plenty of money , she has her own home with more children and goes abroad on holiday every year , even just had an extension built on her house !! , the csa told her how much debt I am in but still are demanding the full amount , how can this be fair when I am in so much debt through illness , this is just not right and they said that my debts are not there problem and said csa is a priority debt, I thought a mortgage arrears , gas , electric , council tax etc where priority debts ? ?

Can anyone help me , are the cms being unreasonable and unfair ??